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

Terms

a(0) =1a(1) =1a(2) =1a(3) =1a(4) =1a(5) =1a(6) =1a(7) =2a(8) =9a(9) =37a(10) =121a(11) =331a(12) =793a(13) =1717a(14) =3434a(15) =6451a(16) =11561a(17) =20129a(18) =34885a(19) =62017a(20) =116281a(21) =232562a(22) =490337a(23) =1062601a(24) =2309385a(25) =4950751a(26) =10381281a(27) =21242341a(28) =42484682a(29) =83411715