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

Terms

a(0) =1a(1) =-9a(2) =26a(3) =-56a(4) =124a(5) =-234a(6) =342a(7) =-448a(8) =702a(9) =-1116a(10) =1330a(11) =-1456a(12) =2196a(13) =-3078a(14) =3224a(15) =-3584a(16) =4912a(17) =-6318a(18) =6858a(19) =-6944a(20) =8892a(21) =-11970a(22) =12166a(23) =-11648a(24) =15500a(25) =-19764a(26) =18954a(27) =-19152a(28) =24388a(29) =-29016