a(n) = Sum_{k=1..n} binomial(floor(n/k)+2,3).

Terms

a(0) =1a(1) =5a(2) =12a(3) =26a(4) =42a(5) =73a(6) =102a(7) =152a(8) =204a(9) =278a(10) =345a(11) =464a(12) =556a(13) =693a(14) =835a(15) =1021a(16) =1175a(17) =1422a(18) =1613a(19) =1907a(20) =2173a(21) =2496a(22) =2773a(23) =3228a(24) =3569a(25) =4015a(26) =4445a(27) =4998a(28) =5434a(29) =6120