Add 1, multiply by 1, add 2, multiply by 2, etc., start with 2.

Terms

a(0) =2a(1) =3a(2) =3a(3) =5a(4) =10a(5) =13a(6) =39a(7) =43a(8) =172a(9) =177a(10) =885a(11) =891a(12) =5346a(13) =5353a(14) =37471a(15) =37479a(16) =299832a(17) =299841a(18) =2698569a(19) =2698579a(20) =26985790a(21) =26985801a(22) =296843811a(23) =296843823a(24) =3562125876a(25) =3562125889a(26) =46307636557a(27) =46307636571a(28) =648306911994a(29) =648306912009