OFFSET
0,2
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1000
FORMULA
a(n) = Sum_{k=1..n+1} 2^(n-k) * k * binomial(n+1,k) * binomial(n+1+k,k).
n * a(n) = 4 * (2*n+1) * a(n-1) - 4 * (n+1) * a(n-2) for n>1.
a(n) = ((n+2)/2) * Sum_{k=0..n} 3^k * binomial(n+1,k) * binomial(n+1,k+1).
a(n) ~ 2^(n - 1/2) * (2 + sqrt(3))^(n + 3/2) * sqrt(n) / (3^(3/4) * sqrt(Pi)). - Vaclav Kotesovec, Jan 26 2020
MATHEMATICA
a[n_] := Sum[2^(n - k) * k * Binomial[n + 1, k] * Binomial[n + 1 + k, k], {k, 1, n + 1}]; Array[a, 21, 0] (* Amiram Eldar, Jan 20 2020 *)
PROG
(PARI) N=20; x='x+O('x^N); Vec(1/(1-8*x+4*x^2)^(3/2))
(PARI) {a(n) = sum(k=1, n+1, 2^(n-k)*k*binomial(n+1, k)*binomial(n+1+k, k))}
(Magma) R<x>:=PowerSeriesRing(Rationals(), 21); Coefficients(R!( 1/(1 - 8*x + 4*x^2)^(3/2))); // Marius A. Burtea, Jan 20 2020
(Magma) [&+[2^(n-k)*k*Binomial(n+1, k)*Binomial(n+k+1, k):k in [1..n+1]]:n in [0..21]]; // Marius A. Burtea, Jan 20 2020
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jan 19 2020
STATUS
approved