a(1) = 1, then subtract, multiply, and add 2, 3, 4; 5, 6, 7; ... in that order.

Terms

a(0) =1a(1) =-1a(2) =-3a(3) =1a(4) =-4a(5) =-24a(6) =-17a(7) =-25a(8) =-225a(9) =-215a(10) =-226a(11) =-2712a(12) =-2699a(13) =-2713a(14) =-40695a(15) =-40679a(16) =-40696a(17) =-732528a(18) =-732509a(19) =-732529a(20) =-15383109a(21) =-15383087a(22) =-15383110a(23) =-369194640a(24) =-369194615a(25) =-369194641a(26) =-9968255307a(27) =-9968255279a(28) =-9968255308a(29) =-299047659240