a(n) = Sum_{i=1..n} i^2*(-1)^ceiling(sqrt(i)).

Terms

a(0) =-1a(1) =3a(2) =12a(3) =28a(4) =3a(5) =-33a(6) =-82a(7) =-146a(8) =-227a(9) =-127a(10) =-6a(11) =138a(12) =307a(13) =503a(14) =728a(15) =984a(16) =695a(17) =371a(18) =10a(19) =-390a(20) =-831a(21) =-1315a(22) =-1844a(23) =-2420a(24) =-3045a(25) =-2369a(26) =-1640a(27) =-856a(28) =-15a(29) =885