a(0) = -1, otherwise a(n) = (-1)^n*(n^3 - 15*n^2 + 2*n - 12)/6.

Terms

a(0) =-1a(1) =4a(2) =-10a(3) =19a(4) =-30a(5) =42a(6) =-54a(7) =65a(8) =-74a(9) =80a(10) =-82a(11) =79a(12) =-70a(13) =54a(14) =-30a(15) =-3a(16) =46a(17) =-100a(18) =166a(19) =-245a(20) =338a(21) =-446a(22) =570a(23) =-711a(24) =870a(25) =-1048a(26) =1246a(27) =-1465a(28) =1706a(29) =-1970