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 A130758 #10 Apr 13 2016 16:49:24
%S A130758 0,1,2,1,4,1,6,1,8,9,10,2,12,2,14,15,16,2,18,2,20,21,22,2,24,25,26,27,
%T A130758 28,2,30,2,32,33,34,35,36,2,38,39,40,2,42,2,44,45,46,2,48,49,50,51,52,
%U A130758 2,54,55,56,57,58,2,60,2,62,63,64,65,66,2,68
%N A130758 a(n) = n if n is not an odd prime number. Otherwise, a(n) = k, where k is the smallest integer such that n < 10^k.
%t A130758 Table[If[OddQ[n]&&PrimeQ[n],IntegerLength[n],n],{n,0,70}] (* _Harvey P. Dale_, Apr 13 2016 *)
%Y A130758 Cf. A000027, A001477, A006005, A131516.
%K A130758 nonn
%O A130758 1,3
%A A130758 _Mohammad K. Azarian_, Aug 17 2007
%E A130758 Offset corrected by _Mohammad K. Azarian_, Nov 19 2008