a(n) = Sum_{k=0..floor(n/2)} binomial(5*n-k,n-2*k).

A371744

a(n) = Sum_{k=0..floor(n/2)} binomial(5*n-k,n-2*k).

Terms

    a(0) =1a(1) =5a(2) =46a(3) =469a(4) =5017a(5) =55177a(6) =617905a(7) =7008264a(8) =80241790a(9) =925457822a(10) =10735707149a(11) =125128265025

External references