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

Terms

a(0) =-1a(1) =6a(2) =-22a(3) =49a(4) =-77a(5) =119a(6) =-225a(7) =358a(8) =-399a(9) =483a(10) =-849a(11) =1139a(12) =-1059a(13) =1349a(14) =-2179a(15) =2500a(16) =-2414a(17) =2885a(18) =-3975a(19) =4971a(20) =-4661a(21) =4663a(22) =-7505a(23) =8819a(24) =-6932a(25) =8454a(26) =-11986a(27) =12438a(28) =-11952a(29) =12744