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

Terms

a(0) =1a(1) =2a(2) =-1a(3) =3a(4) =15a(5) =9a(6) =16a(7) =128a(8) =119a(9) =129a(10) =1419a(11) =1407a(12) =1420a(13) =19880a(14) =19865a(15) =19881a(16) =337977a(17) =337959a(18) =337978a(19) =6759560a(20) =6759539a(21) =6759561a(22) =155469903a(23) =155469879a(24) =155469904a(25) =4042217504a(26) =4042217477a(27) =4042217505a(28) =117224307645a(29) =117224307615