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For questions about sequences of integers. References are often made to the online resource oeis.org.

32 votes
Accepted

Integrality of a sequence formed by sums

Let $A(x) = \sum_{n=1}^\infty a_n x^n$ and let $$S(x) = \sum_{k=0}^\infty (7k+8)\frac{(3k+1)!}{k!\,(2k+3)!} x^k.$$ Then the formula for $a_n$ gives $A(x) = R(x)S(x)$, where $$R(x) = \frac{1}{3}\biggl( …
Ira Gessel's user avatar
4 votes

Integrality of a sequence formed by sums

Here is another proof, inspired by Tewodros Amdeberhan's. We represent the sum as a constant term in a power series. To represent $(7k+8) \frac{(3k+1)!}{k!\,(2k+3)!}$ as a constant term, we need to ex …
Ira Gessel's user avatar
6 votes
Accepted

Closed form for the A110501 (unsigned Genocchi numbers (of first kind) of even index)

This is a known result. To quote from Richard Stanley's Enumerative Combinatorics, Volume 2, second edition, solution to problem 8(e) of Chapter 5, page 115: This is equivalent to a conjecture of J. M …
Ira Gessel's user avatar