This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A117757 #23 Sep 16 2024 14:26:01
%S A117757 2,4,12,36,118,392,1336,4642,16458,59025,213922,781924,2879938,
%T A117757 10673034,39769185,148880193,559658890,2111459404,7991867657,
%U A117757 30336822624,115457945437,440455347499,1683882372217,6450190109521,24752190739937,95142124007068,366264701294309,1411989176124066
%N A117757 Number of primes between 4^n and 4^(n+1).
%H A117757 Amiram Eldar, <a href="/A117757/b117757.txt">Table of n, a(n) for n = 0..45</a>
%e A117757 a(1) = 4 since the primes 5, 7, 11 and 13 lie between 4 and 16.
%p A117757 a:=proc(n) local ct,j: ct:=0: for j from 4^n to 4^(n+1) do if isprime(j)=true then ct:=ct+1 else fi: ct: od: end: seq(a(n),n=0..8); # execution takes hours - _Emeric Deutsch_, Apr 16 2006
%o A117757 (PARI) { for(n=0,30, istrt=4^n ; iend=istrt*4 ; resul=0 ; forprime(p=istrt+1,iend, resul++ ; ) ; print1(resul,",") ; ) ; } \\ _R. J. Mathar_, Apr 21 2006
%o A117757 (PARI) a(n) = primepi(4^(n+1)) - primepi(4^n) \\ _Michel Marcus_, Jun 21 2013
%Y A117757 First difference of A086680.
%Y A117757 Cf. A036378.
%K A117757 nonn
%O A117757 0,1
%A A117757 _Greg Huber_, Apr 14 2006
%E A117757 More terms from Brian Kuehn (brk158(AT)psu.edu), Apr 19 2006
%E A117757 a(23)-a(27) from _Amiram Eldar_, Jun 11 2024