a(n) = Sum_{d divides n} (-1)^(d + n/d) * d^2.

Terms

a(0) =1a(1) =-5a(2) =10a(3) =-13a(4) =26a(5) =-50a(6) =50a(7) =-45a(8) =91a(9) =-130a(10) =122a(11) =-130a(12) =170a(13) =-250a(14) =260a(15) =-173a(16) =290a(17) =-455a(18) =362a(19) =-338a(20) =500a(21) =-610a(22) =530a(23) =-450a(24) =651a(25) =-850a(26) =820a(27) =-650a(28) =842a(29) =-1300