Add 1, multiply by 1, add 2, multiply by 2, etc.; start with 4.

Terms

a(0) =4a(1) =5a(2) =5a(3) =7a(4) =14a(5) =17a(6) =51a(7) =55a(8) =220a(9) =225a(10) =1125a(11) =1131a(12) =6786a(13) =6793a(14) =47551a(15) =47559a(16) =380472a(17) =380481a(18) =3424329a(19) =3424339a(20) =34243390a(21) =34243401a(22) =376677411a(23) =376677423a(24) =4520129076a(25) =4520129089a(26) =58761678157a(27) =58761678171a(28) =822663494394a(29) =822663494409