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 A064557 #3 Mar 30 2012 18:50:18
%S A064557 0,1,2,2,2,2,3,3,3,3,3,3,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,5,5,5,5,5,5,
%T A064557 5,5,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,7,7,7,7,7,7,7,7,8,8,8,8,8,8,8,8,
%U A064557 8,8,8,8,8,8,8,8,8,8,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9
%N A064557 a(n) = # { p | A064553(k) = p prime and k <= n}.
%C A064557 Primes occur in A064553 in natural order but less dense.
%Y A064557 A000720, A064553.
%K A064557 nonn
%O A064557 1,3
%A A064557 _Reinhard Zumkeller_, Sep 21 2001