Number of positive integers <= 2^n of form x^2 + 16*y^2.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =4a(5) =8a(6) =13a(7) =25a(8) =44a(9) =83a(10) =152a(11) =286a(12) =538a(13) =1020a(14) =1942a(15) =3725a(16) =7145a(17) =13781a(18) =26627a(19) =51572a(20) =100099a(21) =194633a(22) =379037a(23) =739250a(24) =1443573a(25) =2822186a(26) =5522889a(27) =10818417a(28) =21209278a(29) =41613288