a(n) = Sum_{k=0..floor(4*n/7)} binomial(k+3,4*n-7*k).

Terms

a(0) =1a(1) =0a(2) =4a(3) =0a(4) =10a(5) =0a(6) =20a(7) =1a(8) =35a(9) =8a(10) =56a(11) =36a(12) =84a(13) =120a(14) =121a(15) =330a(16) =177a(17) =792a(18) =298a(19) =1716a(20) =650a(21) =3433a(22) =1729a(23) =6451a(24) =4823a(25) =11576a(26) =12936a(27) =20264a(28) =32505a(29) =35700