A358365 a(n) = 16^n * Sum_{k=0..n} binomial(-1/2, k)^2.
1, 20, 356, 6096, 102436, 1702480, 28093456, 461273920, 7546019620, 123100218320, 2003738272656, 32557446669120, 528231606378256, 8559878182412096, 138567392514153536, 2241139725237406976, 36219533239041063716, 584958249814679707856, 9441690077748181415696
Offset: 0
Keywords
Programs
-
Maple
a := n -> 16^n*add(binomial(-1/2, k)^2, k = 0..n): seq(a(n), n = 0..18);
-
Mathematica
a[n_] := 16^n * Sum[Binomial[-1/2, k]^2, {k, 0, n}]; Array[a, 19, 0] (* Amiram Eldar, Nov 12 2022 *)
Formula
a(n) = (-64*(2*n - 1)^2*a(n - 2) + 4*(8*n^2 - 4*n + 1)*a(n - 1)) / n^2.
G.f.: hypergeom([1/2, 1/2], [1], 16*x)/(1 - 16*x).
G.f.: 2*EllipticK(4*sqrt(x))/(Pi*(1 - 16*x)).
a(n) ~ (log(n) + gamma + 4*log(2)) * 2^(4*n)/Pi, where gamma is the Euler-Mascheroni constant A001620. - Vaclav Kotesovec, Nov 14 2023