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

Terms

a(0) =1a(1) =3a(2) =6a(3) =16a(4) =39a(5) =99a(6) =248a(7) =622a(8) =1559a(9) =3907a(10) =9793a(11) =24546a(12) =61529a(13) =154230a(14) =386598a(15) =969056a(16) =2429064a(17) =6088760a(18) =15262259a(19) =38256810a(20) =95895601a(21) =240374624a(22) =602529829a(23) =1510318305a(24) =3785806568a(25) =9489609784a(26) =23786924201a(27) =59624976768a(28) =149457652642a(29) =374634777972