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 A089568 #5 Mar 30 2012 17:29:13 %S A089568 13,1,2,19,3,8,15,18,10,17,45,24,22,11,37,5,30,39,81,6,76,57,69,56,84, %T A089568 36,49,48,38,63,148,27,75,239,31,50,171,67,116,282,42,175,23,55,236, %U A089568 70,278,73,90,140,91,9,210,174,126,105,89,94,224,34,114,26,133,143,54,241 %N A089568 a(1) = 13. For n > 1, a(n) is the least unused number such that every concatenation a(n)a(n-1)...a(2)a(1) is prime. %C A089568 Is this a rearrangement of the natural numbers? %Y A089568 Cf. A089710, A089711, A089560-A089573. %K A089568 base,nonn %O A089568 1,1 %A A089568 _Ray Chandler_, Nov 22 2003 %E A089568 Edited by _Charles R Greathouse IV_, Apr 29 2010