a(n) = Sum_{k=0..floor(2*n/7)} binomial(2*k,2*n-7*k).

Terms

a(0) =1a(1) =0a(2) =0a(3) =0a(4) =2a(5) =0a(6) =0a(7) =1a(8) =6a(9) =1a(10) =0a(11) =6a(12) =20a(13) =6a(14) =1a(15) =28a(16) =70a(17) =28a(18) =11a(19) =120a(20) =252a(21) =121a(22) =76a(23) =495a(24) =924a(25) =509a(26) =430a(27) =2003a(28) =3433a(29) =2122