A372018 G.f. A(x) satisfies A(x) = ( 1 + 4*x*A(x)/(1 - x*A(x)) )^(1/2).

1, 2, 4, 10, 30, 98, 336, 1194, 4360, 16258, 61644, 236938, 921102, 3615330, 14307312, 57024426, 228701646, 922283522, 3737497980, 15212318730, 62160993642, 254909413218, 1048717979424, 4327273358250, 17903826642780, 74260741616514, 308724721176676

Offset

0,2

Links

Table of n, a(n) for n=0..26.

Formula

a(n) = (1/(n+1)) * Sum_{k=0..n} 4^k * binomial(n/2+1/2,k) * binomial(n-1,n-k).

D-finite with recurrence n*(n+1)*(n-2)*a(n) -6*(n-2)*(3*n^2-6*n+1)*a(n-2) -27*n*(n-3)*(n-4)*a(n-4)=0. - R. J. Mathar, Apr 22 2024

Conjecture: a(2n+1) = 2*A371364(). - R. J. Mathar, Apr 22 2024

Maple

A372018 := proc(n)
    add(4^k*binomial((n+1)/2, k)*binomial(n-1, k-1), k=0..n) ;
    %/(n+1) ;
end proc:
seq(A372018(n), n=0..60) ; # R. J. Mathar, Apr 22 2024

Prog

(PARI) a(n) = sum(k=0, n, 4^k*binomial(n/2+1/2, k)*binomial(n-1, n-k))/(n+1);

Crossrefs

Cf. A372019, A372020.

Sequence in context: A149836 A003289 A087161 * A360814 A337488 A328358

Adjacent sequences: A372015 A372016 A372017 * A372019 A372020 A372021

Keyword

nonn

Author

Seiichi Manyama, Apr 15 2024

Status

approved