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

Terms

a(0) =1a(1) =-9a(2) =28a(3) =-57a(4) =126a(5) =-252a(6) =344a(7) =-441a(8) =757a(9) =-1134a(10) =1332a(11) =-1596a(12) =2198a(13) =-3096a(14) =3528a(15) =-3513a(16) =4914a(17) =-6813a(18) =6860a(19) =-7182a(20) =9632a(21) =-11988a(22) =12168a(23) =-12348a(24) =15751a(25) =-19782a(26) =20440a(27) =-19608a(28) =24390a(29) =-31752