A139468 a(n) = Sum{k=0..n} C(n,3k+1)^2.

0, 1, 4, 9, 17, 50, 261, 1275, 5028, 17253, 58601, 218042, 876789, 3537847, 13783018, 52301709, 198627921, 767778786, 3010327497, 11824753551, 46200429186, 179787741723, 700285942731, 2738134757118, 10739885115573, 42164261091351, 165467386466802

Offset: 0

Author

N. J. A. Sloane, Jun 12 2008

Keywords

• nonn

Comments

The recurrence is same as for A119363. - Vaclav Kotesovec, Mar 12 2019

Links

• Seiichi Manyama, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A024494, A119363, A139469.

Programs

Mathematica

Table[Sum[Binomial[n,3k+1]^2,{k,0,n}],{n,0,30}] (* Harvey P. Dale, Sep 08 2018 *)

Formula

a(n) ~ 4^n / (3*sqrt(Pi*n)). - Vaclav Kotesovec, Mar 12 2019