Number of positive integers <= 2^n of form 3 x^2 + 9 y^2.

Terms

a(0) =0a(1) =0a(2) =1a(3) =1a(4) =3a(5) =5a(6) =10a(7) =17a(8) =32a(9) =56a(10) =106a(11) =195a(12) =365a(13) =691a(14) =1308a(15) =2495a(16) =4773a(17) =9174a(18) =17671a(19) =34144a(20) =66131a(21) =128330a(22) =249482a(23) =485761a(24) =947206a(25) =1849299a(26) =3614605a(27) =7072464a(28) =13851148a(29) =27150649