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

Terms

a(0) =1a(1) =-1a(2) =2a(3) =8a(4) =3a(5) =9a(6) =63a(7) =55a(8) =64a(9) =640a(10) =629a(11) =641a(12) =8333a(13) =8319a(14) =8334a(15) =133344a(16) =133327a(17) =133345a(18) =2533555a(19) =2533535a(20) =2533556a(21) =55738232a(22) =55738209a(23) =55738233a(24) =1393455825a(25) =1393455799a(26) =1393455826a(27) =39016763128a(28) =39016763099a(29) =39016763129