a(n) = 1/7*( binomial(n,7) - floor(n/7) ).

Terms

a(0) =1a(1) =5a(2) =17a(3) =47a(4) =113a(5) =245a(6) =490a(7) =919a(8) =1634a(9) =2778a(10) =4546a(11) =7198a(12) =11074a(13) =16611a(14) =24363a(15) =35022a(16) =49443a(17) =68671a(18) =93971a(19) =126861a(20) =169148a(21) =222968a(22) =290828a(23) =375653a(24) =480836a(25) =610292a(26) =768516a(27) =960645a(28) =1192525a(29) =1470781