Number of positive integers <= 2^n of form x^2 + 15 y^2.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =5a(5) =9a(6) =16a(7) =27a(8) =52a(9) =91a(10) =173a(11) =322a(12) =606a(13) =1152a(14) =2191a(15) =4191a(16) =8060a(17) =15540a(18) =30018a(19) =58161a(20) =112891a(21) =219479a(22) =427440a(23) =833615a(24) =1627752a(25) =3182068a(26) =6226916a(27) =12196740a(28) =23910690a(29) =46911434