a(n) = floor(sqrt( 2*Pi )^n).

Terms

a(0) =1a(1) =2a(2) =6a(3) =15a(4) =39a(5) =98a(6) =248a(7) =621a(8) =1558a(9) =3906a(10) =9792a(11) =24546a(12) =61528a(13) =154230a(14) =386597a(15) =969056a(16) =2429063a(17) =6088760a(18) =15262258a(19) =38256809a(20) =95895600a(21) =240374623a(22) =602529828a(23) =1510318305a(24) =3785806567a(25) =9489609784a(26) =23786924200a(27) =59624976768a(28) =149457652641a(29) =374634777972