a(n) = Sum_{k=1..n} binomial(k, n mod k).

Terms

a(0) =1a(1) =2a(2) =4a(3) =6a(4) =11a(5) =15a(6) =27a(7) =39a(8) =63a(9) =100a(10) =159a(11) =247a(12) =403a(13) =641a(14) =1023a(15) =1644a(16) =2653a(17) =4264a(18) =6872a(19) =11081a(20) =17895a(21) =28899a(22) =46680a(23) =75420a(24) =121918a(25) =197113a(26) =318728a(27) =515420a(28) =833592a(29) =1348309