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

Terms

a(0) =1a(1) =1a(2) =3a(3) =5a(4) =9a(5) =17a(6) =31a(7) =54a(8) =97a(9) =172a(10) =306a(11) =542a(12) =961a(13) =1704a(14) =3020a(15) =5353a(16) =9488a(17) =16817a(18) =29809a(19) =52835a(20) =93648a(21) =165986a(22) =294204a(23) =521463a(24) =924269a(25) =1638224a(26) =2903677a(27) =5146633a(28) =9122171a(29) =16168627