a(n) = Sum_{d divides n} (-1)^(n/d+1)*d^3.

Terms

a(0) =1a(1) =7a(2) =28a(3) =55a(4) =126a(5) =196a(6) =344a(7) =439a(8) =757a(9) =882a(10) =1332a(11) =1540a(12) =2198a(13) =2408a(14) =3528a(15) =3511a(16) =4914a(17) =5299a(18) =6860a(19) =6930a(20) =9632a(21) =9324a(22) =12168a(23) =12292a(24) =15751a(25) =15386a(26) =20440a(27) =18920a(28) =24390a(29) =24696