a(n) = Sum_{k=0..n} binomial(2*n+1,5*k).

Terms

a(0) =1a(1) =1a(2) =2a(3) =22a(4) =127a(5) =474a(6) =1574a(7) =6008a(8) =25773a(9) =107883a(10) =427351a(11) =1669801a(12) =6643782a(13) =26789257a(14) =107746282a(15) =430470899a(16) =1717012749a(17) =6863694378a(18) =27481113638a(19) =109996928003a(20) =439924466026