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

Terms

a(0) =1a(1) =3a(2) =10a(3) =16a(4) =32a(5) =49a(6) =78a(7) =100a(8) =152a(9) =194a(10) =261a(11) =318a(12) =410a(13) =489a(14) =631a(15) =717a(16) =871a(17) =1014a(18) =1205a(19) =1351a(20) =1617a(21) =1806a(22) =2083a(23) =2300a(24) =2641a(25) =2903a(26) =3333a(27) =3612a(28) =4048a(29) =4450