a(n) = Sum_{k=0..floor(4*n/7)} binomial(k+1,4*n-7*k).

Terms

a(0) =1a(1) =0a(2) =2a(3) =0a(4) =3a(5) =0a(6) =4a(7) =1a(8) =5a(9) =6a(10) =6a(11) =21a(12) =7a(13) =56a(14) =9a(15) =126a(16) =19a(17) =252a(18) =65a(19) =462a(20) =231a(21) =793a(22) =727a(23) =1301a(24) =2015a(25) =2107a(26) =5019a(27) =3563a(28) =11456a(29) =6748