Number of primes between 4^n and 4^(n+1).

Terms

a(0) =2a(1) =4a(2) =12a(3) =36a(4) =118a(5) =392a(6) =1336a(7) =4642a(8) =16458a(9) =59025a(10) =213922a(11) =781924a(12) =2879938a(13) =10673034a(14) =39769185a(15) =148880193a(16) =559658890a(17) =2111459404a(18) =7991867657a(19) =30336822624a(20) =115457945437a(21) =440455347499