OFFSET
0,2
LINKS
FORMULA
a(n) = A183065(2*n,n).
a(n) = [x^(2*n)*y^n] Sum_{m >= 0} (4*m)!/m!^4 * x^(2*m)*y^m/(1-x-x*y)^(4*m+1).
From Peter Bala, Jul 15 2024: (Start)
a(n) = binomial(2*n, n)*Sum_{k = 0..n} binomial(n, k)^2*binomial(2*n+2*k, 2*k)* binomial(2*k, k) = Sum_{k = 0..n} (2*n+2*k)!/(k!^4*(n-k)!^2). Cf. A002897(n) = Sum_{k = 0..n} (2*n+k)!/(k!^3*(n-k)!^2) and A005258(n) = n!*Sum_{k = 0..n} (n+k)!/(k!^3*(n-k)!^2).
a(n) = binomial(2*n, n)*hypergeom([-n, -n, n+1, n+1/2], [1, 1, 1], 4).
Conjecture: the supercongruence a(n*p^r) == a(n*p^(r-1)) (mod p^(2*r)) holds for all primes p and positive integers n and r (End)
a(n) ~ sqrt(3) * (2 + sqrt(6))^(4*n + 3/2) / (16*Pi^2*n^2). - Vaclav Kotesovec, Jul 16 2024
MAPLE
seq(simplify(binomial(2*n, n)*hypergeom([-n, -n, n+1, n+1/2], [1, 1, 1], 4)), n = 0..20);
PROG
(PARI) {a(n)=polcoeff(polcoeff(sum(m=0, 2*n, (4*m)!/m!^4*x^(2*m)*y^m/(1-x-x*y+x*O(x^(2*n)))^(4*m+1)), 2*n, x), n, y)}
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Paul D. Hanna, Dec 22 2010
STATUS
approved