a(1) = 1, a(2) = 3; a(n) = n^2 * Sum_{d|n, d < n} (-1)^(n/d) a(d) / d^2.

Terms

a(0) =1a(1) =3a(2) =-9a(3) =28a(4) =-25a(5) =-27a(6) =-49a(7) =224a(8) =0a(9) =-75a(10) =-121a(11) =-252a(12) =-169a(13) =-147a(14) =225a(15) =1792a(16) =-289a(17) =0a(18) =-361a(19) =-700a(20) =441a(21) =-363a(22) =-529a(23) =-2016a(24) =0a(25) =-507a(26) =0a(27) =-1372a(28) =-841a(29) =675