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

Terms

a(0) =1a(1) =2a(2) =4a(3) =10a(4) =24a(5) =54a(6) =120a(7) =266a(8) =593a(9) =1317a(10) =2926a(11) =6501a(12) =14441a(13) =32081a(14) =71266a(15) =158315a(16) =351688a(17) =781255a(18) =1735512a(19) =3855339a(20) =8564410a(21) =19025337a(22) =42263673a(23) =93886277a(24) =208562871a(25) =463310210a(26) =1029216515a(27) =2286344247a(28) =5078979923a(29) =11282656623