a(n) = n * Pell(n).

Terms

a(0) =0a(1) =1a(2) =4a(3) =15a(4) =48a(5) =145a(6) =420a(7) =1183a(8) =3264a(9) =8865a(10) =23780a(11) =63151a(12) =166320a(13) =434993a(14) =1130948a(15) =2925375a(16) =7533312a(17) =19323713a(18) =49395780a(19) =125877071a(20) =319888560a(21) =810893265a(22) =2050891876a(23) =5176349663a(24) =13040153280a(25) =32793453025a(26) =82337215012a(27) =206424991215