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 A154521 #8 Jul 16 2015 21:49:04
%S A154521 4,6,9,0,4,5,8,0,2,6,7,2,4,5,8,2,6,8,1,4,5,8,2,5,0,4,5,7,8,1,0,2,5,6,
%T A154521 2,0,0,1,1,4,6,1,0,2,2,2,2,3,4,3,6,0,4,4,6,8,2,5,5,6,5,1,6,9,7,1,7,8,
%U A154521 4,8,6,8,9,9,9,0,2,0,6,0,3,1,7,1,2,1,4,2,0,3,2,7,4,3,4,7,9,4,5,6,6,8,2,4,7
%N A154521 The prime(n)-th digit of the concatenated positive nonprimes.
%C A154521 The digits of A129808 at prime indices.
%F A154521 a(n) = A129808(prime(n)) .
%p A154521 a129808 := [1] : for n from 4 to 400 do if not isprime(n) then a129808 := [op(a129808), op(ListTools[Reverse](convert(n,base,10))) ] ; fi; od:
%p A154521 for n from 1 do p := ithprime(n) ; printf("%d,", op(p,a129808) ) ; od: # _R. J. Mathar_, Aug 03 2009
%Y A154521 Cf. A000040, A154513, A154520.
%K A154521 nonn,base,less
%O A154521 1,1
%A A154521 _Juri-Stepan Gerasimov_, Jan 11 2009
%E A154521 Edited and corrected by _R. J. Mathar_, Aug 03 2009