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

Terms

a(0) =0a(1) =1a(2) =4a(3) =11a(4) =21a(5) =40a(6) =61a(7) =96a(8) =135a(9) =191a(10) =246a(11) =337a(12) =415a(13) =528a(14) =646a(15) =801a(16) =937a(17) =1145a(18) =1316a(19) =1568a(20) =1802a(21) =2089a(22) =2342a(23) =2737a(24) =3047a(25) =3451a(26) =3841a(27) =4338a(28) =4744a(29) =5358