a(n) = Sum_{k=0..floor(3*n/17)} binomial(3*n-16*k,k).

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =3a(7) =6a(8) =9a(9) =12a(10) =15a(11) =18a(12) =27a(13) =45a(14) =72a(15) =108a(16) =153a(17) =208a(18) =290a(19) =426a(20) =643a(21) =968a(22) =1428a(23) =2055a(24) =2931a(25) =4218a(26) =6159a(27) =9078a(28) =13380a(29) =19572