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

Terms

a(0) =1a(1) =1a(2) =6a(3) =21a(4) =71a(5) =251a(6) =882a(7) =3088a(8) =10829a(9) =37975a(10) =133146a(11) =466852a(12) =1636944a(13) =5739647a(14) =20125051a(15) =70564951a(16) =247423522a(17) =867546829a(18) =3041899638a(19) =10665883415a(20) =37398034921a(21) =131129599227a(22) =459782762029