a(n) = Sum_{k=1..n} binomial(floor(n/k)+3,4).

Terms

a(0) =1a(1) =6a(2) =17a(3) =42a(4) =78a(5) =149a(6) =234a(7) =379a(8) =555a(9) =815a(10) =1102a(11) =1557a(12) =2013a(13) =2662a(14) =3388a(15) =4349a(16) =5319a(17) =6695a(18) =8026a(19) =9846a(20) =11712a(21) =14027a(22) =16328a(23) =19503a(24) =22464a(25) =26200a(26) =30030a(27) =34759a(28) =39255a(29) =45221