a(1) = 1, otherwise a(n) = floor(e^(n+1)/(e^2 + 1)).

Terms

a(0) =0a(1) =1a(2) =2a(3) =6a(4) =17a(5) =48a(6) =130a(7) =355a(8) =965a(9) =2625a(10) =7137a(11) =19400a(12) =52736a(13) =143353a(14) =389676a(15) =1059250a(16) =2879340a(17) =7826860a(18) =21275611a(19) =57833108a(20) =157206689a(21) =427332086a(22) =1161609045a(23) =3157580759a(24) =8583194400a(25) =23331541370a(26) =63421704936a(27) =172398068058a(28) =468626535665