a(n) = Sum_{k=1..n} (-1)^(k-1) * binomial(floor(n/k)+4,5).

Terms

a(0) =1a(1) =5a(2) =21a(3) =50a(4) =121a(5) =236a(6) =447a(7) =736a(8) =1247a(9) =1896a(10) =2898a(11) =4151a(12) =5972a(13) =8146a(14) =11292a(15) =14797a(16) =19643a(17) =25248a(18) =32564a(19) =40663a(20) =51515a(21) =63168a(22) =78119a(23) =94452a(24) =114998a(25) =136933a(26) =164849a(27) =193753a(28) =229714a(29) =268334