a(n) = Sum_{k=0..floor(3*n/5)} binomial(k+1,3*n-5*k).

Terms

a(0) =1a(1) =0a(2) =2a(3) =0a(4) =3a(5) =1a(6) =4a(7) =5a(8) =5a(9) =15a(10) =7a(11) =35a(12) =15a(13) =70a(14) =44a(15) =127a(16) =129a(17) =221a(18) =340a(19) =396a(20) =804a(21) =781a(22) =1742a(23) =1716a(24) =3550a(25) =4005a(26) =7009a(27) =9390a(28) =13835a(29) =21421