Number of positive integers <= 2^n of form x^2 + 9 y^2.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =6a(5) =8a(6) =18a(7) =30a(8) =57a(9) =103a(10) =194a(11) =360a(12) =682a(13) =1292a(14) =2464a(15) =4721a(16) =9078a(17) =17481a(18) =33808a(19) =65485a(20) =127116a(21) =247179a(22) =481426a(23) =938950a(24) =1833572a(25) =3584679a(26) =7015237a(27) =13741715a(28) =26940645a(29) =52858250