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

Terms

a(0) =1a(1) =3a(2) =9a(3) =5a(4) =10a(5) =60a(6) =53a(7) =61a(8) =549a(9) =539a(10) =550a(11) =6600a(12) =6587a(13) =6601a(14) =99015a(15) =98999a(16) =99016a(17) =1782288a(18) =1782269a(19) =1782289a(20) =37428069a(21) =37428047a(22) =37428070a(23) =898273680a(24) =898273655a(25) =898273681a(26) =24253389387a(27) =24253389359a(28) =24253389388a(29) =727601681640