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#binomial — Public Fediverse posts

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  1. I'm doing some symmetric monoidal algebra that involves careful counting of some signs of certain permutations. The work depends on a couple of combinatorial identities that I haven't seen anywhere else—do you recognize these (below)?!

    The identities involve the "choose two" binomial coefficients.
    For ease of typing, I'll use this notation:

    [a;2] = binomial(a,2) = a·(a-1)/2
    (read "a choose 2")

    The two identities are

    (I1):
    [a+b;2] = [a;2] + [b;2] + ab

    and

    (I2):
    [ab;2] = a[b;2] + b[a;2] + 2[a;2][b;2]

    In particular, (I2) means there is a mod 2 congruence
    [ab;2] ≡ a[b;2] + b[a;2]
    and that's the form that has been particularly useful for me.

    Neither of these identities are hard to prove directly from the definition, and they hold for positive *and negative* integers a and b. (That extension to all integers is important for my applications too.)

    I've done some internet searching (wikipedia [1,2] and other general references), but I haven't found mention of these particular identities. So, I'm wondering if anyone here recognizes them. (Boosts appreciated!)

    Note: These particular binomial coefficients [a;2], for positive a, are also called *triangular numbers*. I'll rewrite (I1) and (I2) in terms of triangular numbers in the next post, in case people will recognize that alternate form (but I doubt it).

    [1] en.wikipedia.org/wiki/Binomial
    [2] en.wikipedia.org/wiki/Triangul

    (1/2)

    #binomial #triangular #PascalsTriangle

  2. I'm doing some symmetric monoidal algebra that involves careful counting of some signs of certain permutations. The work depends on a couple of combinatorial identities that I haven't seen anywhere else—do you recognize these (below)?!

    The identities involve the "choose two" binomial coefficients.
    For ease of typing, I'll use this notation:

    [a;2] = binomial(a,2) = a·(a-1)/2
    (read "a choose 2")

    The two identities are

    (I1):
    [a+b;2] = [a;2] + [b;2] + ab

    and

    (I2):
    [ab;2] = a[b;2] + b[a;2] + 2[a;2][b;2]

    In particular, (I2) means there is a mod 2 congruence
    [ab;2] ≡ a[b;2] + b[a;2]
    and that's the form that has been particularly useful for me.

    Neither of these identities are hard to prove directly from the definition, and they hold for positive *and negative* integers a and b. (That extension to all integers is important for my applications too.)

    I've done some internet searching (wikipedia [1,2] and other general references), but I haven't found mention of these particular identities. So, I'm wondering if anyone here recognizes them. (Boosts appreciated!)

    Note: These particular binomial coefficients [a;2], for positive a, are also called *triangular numbers*. I'll rewrite (I1) and (I2) in terms of triangular numbers in the next post, in case people will recognize that alternate form (but I doubt it).

    [1] en.wikipedia.org/wiki/Binomial
    [2] en.wikipedia.org/wiki/Triangul

    (1/2)

    #binomial #triangular #PascalsTriangle

  3. I'm doing some symmetric monoidal algebra that involves careful counting of some signs of certain permutations. The work depends on a couple of combinatorial identities that I haven't seen anywhere else—do you recognize these (below)?!

    The identities involve the "choose two" binomial coefficients.
    For ease of typing, I'll use this notation:

    [a;2] = binomial(a,2) = a·(a-1)/2
    (read "a choose 2")

    The two identities are

    (I1):
    [a+b;2] = [a;2] + [b;2] + ab

    and

    (I2):
    [ab;2] = a[b;2] + b[a;2] + 2[a;2][b;2]

    In particular, (I2) means there is a mod 2 congruence
    [ab;2] ≡ a[b;2] + b[a;2]
    and that's the form that has been particularly useful for me.

    Neither of these identities are hard to prove directly from the definition, and they hold for positive *and negative* integers a and b. (That extension to all integers is important for my applications too.)

    I've done some internet searching (wikipedia [1,2] and other general references), but I haven't found mention of these particular identities. So, I'm wondering if anyone here recognizes them. (Boosts appreciated!)

    Note: These particular binomial coefficients [a;2], for positive a, are also called *triangular numbers*. I'll rewrite (I1) and (I2) in terms of triangular numbers in the next post, in case people will recognize that alternate form (but I doubt it).

    [1] en.wikipedia.org/wiki/Binomial
    [2] en.wikipedia.org/wiki/Triangul

    (1/2)

    #binomial #triangular #PascalsTriangle

  4. I'm doing some symmetric monoidal algebra that involves careful counting of some signs of certain permutations. The work depends on a couple of combinatorial identities that I haven't seen anywhere else—do you recognize these (below)?!

    The identities involve the "choose two" binomial coefficients.
    For ease of typing, I'll use this notation:

    [a;2] = binomial(a,2) = a·(a-1)/2
    (read "a choose 2")

    The two identities are

    (I1):
    [a+b;2] = [a;2] + [b;2] + ab

    and

    (I2):
    [ab;2] = a[b;2] + b[a;2] + 2[a;2][b;2]

    In particular, (I2) means there is a mod 2 congruence
    [ab;2] ≡ a[b;2] + b[a;2]
    and that's the form that has been particularly useful for me.

    Neither of these identities are hard to prove directly from the definition, and they hold for positive *and negative* integers a and b. (That extension to all integers is important for my applications too.)

    I've done some internet searching (wikipedia [1,2] and other general references), but I haven't found mention of these particular identities. So, I'm wondering if anyone here recognizes them. (Boosts appreciated!)

    Note: These particular binomial coefficients [a;2], for positive a, are also called *triangular numbers*. I'll rewrite (I1) and (I2) in terms of triangular numbers in the next post, in case people will recognize that alternate form (but I doubt it).

    [1] en.wikipedia.org/wiki/Binomial
    [2] en.wikipedia.org/wiki/Triangul

    (1/2)

    #binomial #triangular #PascalsTriangle

  5. I'm doing some symmetric monoidal algebra that involves careful counting of some signs of certain permutations. The work depends on a couple of combinatorial identities that I haven't seen anywhere else—do you recognize these (below)?!

    The identities involve the "choose two" binomial coefficients.
    For ease of typing, I'll use this notation:

    [a;2] = binomial(a,2) = a·(a-1)/2
    (read "a choose 2")

    The two identities are

    (I1):
    [a+b;2] = [a;2] + [b;2] + ab

    and

    (I2):
    [ab;2] = a[b;2] + b[a;2] + 2[a;2][b;2]

    In particular, (I2) means there is a mod 2 congruence
    [ab;2] ≡ a[b;2] + b[a;2]
    and that's the form that has been particularly useful for me.

    Neither of these identities are hard to prove directly from the definition, and they hold for positive *and negative* integers a and b. (That extension to all integers is important for my applications too.)

    I've done some internet searching (wikipedia [1,2] and other general references), but I haven't found mention of these particular identities. So, I'm wondering if anyone here recognizes them. (Boosts appreciated!)

    Note: These particular binomial coefficients [a;2], for positive a, are also called *triangular numbers*. I'll rewrite (I1) and (I2) in terms of triangular numbers in the next post, in case people will recognize that alternate form (but I doubt it).

    [1] en.wikipedia.org/wiki/Binomial
    [2] en.wikipedia.org/wiki/Triangul

    (1/2)

    #binomial #triangular #PascalsTriangle

  6. Try to prove the following two results that relate the harmonic numbers to the golden ratio. Have an excellent weekend.

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^n}=2\sqrt5\ln\varphi\]

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^nn}=\frac{2\pi^2}{15}-2\ln^2\varphi\]

    where \(\varphi=\frac{1+\sqrt5}2\) is the golden ratio; and \(H_n=\left(1+\frac12+\frac13+\ldots+\frac1n\right)\) is the \(n\)-th harmonic number.

    #GoldenRatio #HarmonicNumbers #HarmonicNumber #Logarithm #Pi #Summation #Math #Sum #InfiniteSum #Binomial #BinomialCoefficient #Maths #WeekendChallenge

  7. One day, one decomposition
    A138389: Binomial primes: positive integers n such that every i not coprime to n and not exceeding n/2 does not divide binomial(n-i-1,i-1)

    3D graph, threejs - webGL ➡️ decompwlj.com/3Dgraph/Binomial
    2D graph, first 500 terms ➡️ decompwlj.com/2Dgraph500terms/

    #decompwlj #math #mathematics #sequence #OEIS #javascript #php #3D #numbers #binomial #primes #PrimeNumbers #coprime #graph #threejs #webGL

  8. In the process I also thought of a #binomial #coefficient interpretation for choosing k things out of a bag of n objects when the objects can be put back and picked again. In probability problems, this is referred to as picking "with replacement".

    Usually, when we say, n choose k, we do not allow repeated choices, every chosen object has to be chosen once. In this case, I want to allow replacements but at the same time, I want to keep using my trusted n choose k idea.

    Here's my way around this: We'll still be picking k things, but we'll pick them not from 1 to n but from the set {1, 2, ..., 𝑛, 𝑟₁, 𝑟₂, ..., 𝑟ₖ₋₁}. That is, in addition to the n objects, we add what I'm calling "replacement tokens" 𝑟ₓ. If any of the 𝑟ₓ gets picked, then it is interpreted as the 𝑥th choice was put back and you are now choosing to pick that again. Since the 𝑘th choice is not put back, we only need replacement tokens for choices 1 to k-1.

    With these replacement tokens, the problem becomes a standard choose k things out of this set, which we can resolve using the binomial coefficient to get: \({ n+k-1 \choose k }\).

    I believe the standard approach to this is via #StarsAndBars but I liked the idea of this "replacement token". Admittedly, I didn't want to use stars and bars here and made up some stuff which I happened to like. :)

    #math #counting #proof

  9. Le fun est total.

    (c'est un vrai jeu)
    (enfin c'est un logiciel, que j'ai acheté avec mon argent, dans le but de me détendre, sur steam)

    #infiniteturtles #zachtronics #zachlike #binomial

  10. One day, one decomposition
    A138389: Binomial primes: positive integers n such that every i not coprime to n and not exceeding n/2 does not divide binomial(n-i-1,i-1)

    3D graph, threejs - webGL ➡️ decompwlj.com/3Dgraph/Binomial
    2D graph, first 500 terms ➡️ decompwlj.com/2Dgraph500terms/

    #decompwlj #math #mathematics #sequence #OEIS #javascript #php #3D #numbers #binomial #primes #PrimeNumbers #coprime #graph #threejs #webGL

  11. One day, one decomposition
    A138389: Binomial primes: positive integers n such that every i not coprime to n and not exceeding n/2 does not divide binomial(n-i-1,i-1)

    3D graph, threejs - webGL ➡️ decompwlj.com/3Dgraph/Binomial
    2D graph, first 500 terms ➡️ decompwlj.com/2Dgraph500terms/

    #decompwlj #math #mathematics #sequence #OEIS #javascript #php #3D #numbers #binomial #primes #PrimeNumbers #coprime #graph #threejs #webGL

  12. One day, one decomposition
    A138389: Binomial primes: positive integers n such that every i not coprime to n and not exceeding n/2 does not divide binomial(n-i-1,i-1)

    3D graph, threejs - webGL ➡️ decompwlj.com/3Dgraph/Binomial
    2D graph, first 500 terms ➡️ decompwlj.com/2Dgraph500terms/

    #decompwlj #math #mathematics #sequence #OEIS #javascript #php #3D #numbers #binomial #primes #PrimeNumbers #coprime #graph #threejs #webGL

  13. One day, one decomposition
    A138389: Binomial primes: positive integers n such that every i not coprime to n and not exceeding n/2 does not divide binomial(n-i-1,i-1)

    3D graph, threejs - webGL ➡️ decompwlj.com/3Dgraph/Binomial
    2D graph, first 500 terms ➡️ decompwlj.com/2Dgraph500terms/

    #decompwlj #math #mathematics #sequence #OEIS #javascript #php #3D #numbers #binomial #primes #PrimeNumbers #coprime #graph #threejs #webGL

  14. Try to prove the following two results that relate the harmonic numbers to the golden ratio. Have an excellent weekend.

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^n}=2\sqrt5\ln\varphi\]

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^nn}=\frac{2\pi^2}{15}-2\ln^2\varphi\]

    where \(\varphi=\frac{1+\sqrt5}2\) is the golden ratio; and \(H_n=\left(1+\frac12+\frac13+\ldots+\frac1n\right)\) is the \(n\)-th harmonic number.

    #GoldenRatio #HarmonicNumbers #HarmonicNumber #Logarithm #Pi #Summation #Math #Sum #InfiniteSum #Binomial #BinomialCoefficient #Maths #WeekendChallenge

  15. Try to prove the following two results that relate the harmonic numbers to the golden ratio. Have an excellent weekend.

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^n}=2\sqrt5\ln\varphi\]

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^nn}=\frac{2\pi^2}{15}-2\ln^2\varphi\]

    where \(\varphi=\frac{1+\sqrt5}2\) is the golden ratio; and \(H_n=\left(1+\frac12+\frac13+\ldots+\frac1n\right)\) is the \(n\)-th harmonic number.

    #GoldenRatio #HarmonicNumbers #HarmonicNumber #Logarithm #Pi #Summation #Math #Sum #InfiniteSum #Binomial #BinomialCoefficient #Maths #WeekendChallenge

  16. Try to prove the following two results that relate the harmonic numbers to the golden ratio. Have an excellent weekend.

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^n}=2\sqrt5\ln\varphi\]

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^nn}=\frac{2\pi^2}{15}-2\ln^2\varphi\]

    where \(\varphi=\frac{1+\sqrt5}2\) is the golden ratio; and \(H_n=\left(1+\frac12+\frac13+\ldots+\frac1n\right)\) is the \(n\)-th harmonic number.

    #GoldenRatio #HarmonicNumbers #HarmonicNumber #Logarithm #Pi #Summation #Math #Sum #InfiniteSum #Binomial #BinomialCoefficient #Maths #WeekendChallenge

  17. Try to prove the following two results that relate the harmonic numbers to the golden ratio. Have an excellent weekend.

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^n}=2\sqrt5\ln\varphi\]

    \[\displaystyle\sum_{n=1}^\infty\binom{2n}n\dfrac{H_n}{5^nn}=\frac{2\pi^2}{15}-2\ln^2\varphi\]

    where \(\varphi=\frac{1+\sqrt5}2\) is the golden ratio; and \(H_n=\left(1+\frac12+\frac13+\ldots+\frac1n\right)\) is the \(n\)-th harmonic number.

    #GoldenRatio #HarmonicNumbers #HarmonicNumber #Logarithm #Pi #Summation #Math #Sum #InfiniteSum #Binomial #BinomialCoefficient #Maths #WeekendChallenge

  18. In the process I also thought of a #binomial #coefficient interpretation for choosing k things out of a bag of n objects when the objects can be put back and picked again. In probability problems, this is referred to as picking "with replacement".

    Usually, when we say, n choose k, we do not allow repeated choices, every chosen object has to be chosen once. In this case, I want to allow replacements but at the same time, I want to keep using my trusted n choose k idea.

    Here's my way around this: We'll still be picking k things, but we'll pick them not from 1 to n but from the set {1, 2, ..., 𝑛, 𝑟₁, 𝑟₂, ..., 𝑟ₖ₋₁}. That is, in addition to the n objects, we add what I'm calling "replacement tokens" 𝑟ₓ. If any of the 𝑟ₓ gets picked, then it is interpreted as the 𝑥th choice was put back and you are now choosing to pick that again. Since the 𝑘th choice is not put back, we only need replacement tokens for choices 1 to k-1.

    With these replacement tokens, the problem becomes a standard choose k things out of this set, which we can resolve using the binomial coefficient to get: \({ n+k-1 \choose k }\).

    I believe the standard approach to this is via #StarsAndBars but I liked the idea of this "replacement token". Admittedly, I didn't want to use stars and bars here and made up some stuff which I happened to like. :)

    #math #counting #proof

  19. In this video, we look at binomial expressions using synonyms (words with same or similar meanings).

    This is the second video in a short series on binomial expressions.

    youtu.be/3FRLM5-I9pY

  20. In this video, we look at binomial expressions using synonyms (words with same or similar meanings).

    This is the second video in a short series on binomial expressions.

    #synonyms #LearnEnglish #binomial #expressions #EFL #ESL #daybreakenglish

    youtu.be/3FRLM5-I9pY

  21. In this video, we look at binomial expressions using antonyms (words that are opposites).

    But wait, what's a binomial expression?

    youtu.be/kjknk1UpHAE

  22. In this video, we look at binomial expressions using antonyms (words that are opposites).

    But wait, what's a binomial expression?

    #antonyms #LearnEnglish #binomial #expressions #EFL #ESL #DaybreakEnglish

    youtu.be/kjknk1UpHAE

  23. Le fun est total.

    (c'est un vrai jeu)
    (enfin c'est un logiciel, que j'ai acheté avec mon argent, dans le but de me détendre, sur steam)

    #infiniteturtles #zachtronics #zachlike #binomial

  24. Le fun est total.

    (c'est un vrai jeu)
    (enfin c'est un logiciel, que j'ai acheté avec mon argent, dans le but de me détendre, sur steam)

    #infiniteturtles #zachtronics #zachlike #binomial