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

Terms

a(0) =0a(1) =0a(2) =1a(3) =4a(4) =10a(5) =21a(6) =36a(7) =60a(8) =89a(9) =131a(10) =176a(11) =245a(12) =311a(13) =404a(14) =502a(15) =631a(16) =751a(17) =926a(18) =1079a(19) =1295a(20) =1501a(21) =1756a(22) =1987a(23) =2330a(24) =2612a(25) =2978a(26) =3332a(27) =3779a(28) =4157a(29) =4707