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 A192064 #24 Feb 13 2015 00:27:01 %S A192064 0,1,2,2,1,2,2,1,1,2,2,1,2,2,1,0,1,3,3,2,3,3,2,2,2,0,1,0,0,1,0,2,2,2, %T A192064 0,1,3,2,0,2,0,2,3,0,1,0,1,0,0,0,2,0,1,0,2,1,3,3,2,1,0,3,1,1,1,1,2,5, %U A192064 1,1,1,0,0,1,3,0,2,2,1 %N A192064 Number of primes in the range [2^n-n, 2^n]. %e A192064 a(0)=0 because [2^0-0, 2^0]=[1, 1], %e A192064 a(1)=1 because 2 in range [2^1-1, 2^1]=[1,2], %e A192064 a(2)=2 because 2, 3 in range [2^2-2, 2^2]=[2, 4], %e A192064 a(3)=2 because 5, 7 in range [2^3-3, 2^3]=[5, 8], %e A192064 a(4)=1 because 13 in range [2^4-4, 2^4]=[12, 16], %e A192064 a(5)=2 because 29, 31 in range [2^5-5, 2^5]=[27, 32]. %p A192064 A192064 := proc(n) numtheory[pi](2^n)-numtheory[pi](2^n-n-1) ; end proc: # _R. J. Mathar_, Jul 07 2011 %o A192064 (PARI) a(n)=sum(k=2^n-n,2^n,isprime(k)) \\ _Charles R Greathouse IV_, Jul 03 2011 %K A192064 nonn %O A192064 0,3 %A A192064 _Juri-Stepan Gerasimov_, Jul 03 2011 %E A192064 Corrected and extended by _Charles R Greathouse IV_, Jul 03 2011