a(n) = Sum_{k=0..floor(3*n/5)} binomial(k+2,3*n-5*k).

Terms

a(0) =1a(1) =0a(2) =3a(3) =0a(4) =6a(5) =1a(6) =10a(7) =6a(8) =15a(9) =21a(10) =22a(11) =56a(12) =37a(13) =126a(14) =81a(15) =253a(16) =210a(17) =474a(18) =550a(19) =870a(20) =1354a(21) =1651a(22) =3096a(23) =3367a(24) =6646a(25) =7372a(26) =13655a(27) =16762a(28) =27490a(29) =38183