OFFSET
0,2
COMMENTS
a(n) = B(n,2*n,n) in the notation of Straub, equation 24. It follows from Straub, Theorem 3.2, that the supercongruences a(n*p^k) == a(n*p^(k-1)) (mod p^(3*k)) hold for all primes p >= 5 and all positive integers n and k.
More generally, for positive integers r and s the sequence {A108625(r*n, s*n) : n >= 0} satisfies the same supercongruences.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..500
FORMULA
a(n) = Sum_{k = 0..n} binomial(n, k)^2 * binomial(2*n+k, n).
a(n) = Sum_{k = 0..n} (-1)^(n+k)* binomial(n, k)*binomial(2*n+k, n)^2.
a(n) = hypergeom( [-n, -2*n, n+1], [1, 1], 1).
a(n) = [x^(2*n)] 1/(1 - x)*Legendre_P(n, (1 + x)/(1 - x)).
P-recursive: 4*(2*n - 1)^2*n^2*(85*n^2 - 235*n + 163)*a(n) = (29665*n^6 - 141345*n^5 + 264772*n^4 - 249181*n^3 + 124975*n^2 - 31902*n + 3276)*a(n-1) + 4*(2*n - 3)^2*(n-1)^2*(85*n^2 - 65*n + 13)*a(n-2) with a(0) = 1 and a(1) = 5.
a(n) = Sum_{k = 0..n} binomial(n, k)*binomial(n+k, k)*binomial(2*n, k). - Peter Bala, Feb 25 2024
a(n) ~ sqrt(13 + 53/sqrt(17)) * (349 + 85*sqrt(17))^n / (Pi * n * 2^(5*n + 5/2)). - Vaclav Kotesovec, Apr 26 2024
MAPLE
MATHEMATICA
Table[HypergeometricPFQ[{-n, -2*n, n+1}, {1, 1}, 1], {n, 0, 30}] (* G. C. Greubel, Oct 05 2023 *)
PROG
(Magma)
A363867:= func< n | (&+[Binomial(n, j)^2*Binomial(2*n+j, n): j in [0..n]]) >;
[A363867(n): n in [0..30]]; // G. C. Greubel, Oct 05 2023
(SageMath)
def A363867(n): return sum(binomial(n, j)^2*binomial(2*n+j, n) for j in range(n+1))
[A363867(n) for n in range(31)] # G. C. Greubel, Oct 05 2023
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Peter Bala, Jun 27 2023
STATUS
approved