a(n) = floor(e^n).

Terms

a(0) =1a(1) =2a(2) =7a(3) =20a(4) =54a(5) =148a(6) =403a(7) =1096a(8) =2980a(9) =8103a(10) =22026a(11) =59874a(12) =162754a(13) =442413a(14) =1202604a(15) =3269017a(16) =8886110a(17) =24154952a(18) =65659969a(19) =178482300a(20) =485165195a(21) =1318815734a(22) =3584912846a(23) =9744803446a(24) =26489122129a(25) =72004899337a(26) =195729609428a(27) =532048240601