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 A117623 #8 Mar 18 2014 11:52:32
%S A117623 3,2,4,-1,5,-6,7,9,-12,8,10,-14,11,13,-22,15,16,-28,17,18,-34,20,21,
%T A117623 -38,19,24,-42,25,-23,26,27,-49,30,29,-57,31,33,-63,35,32,-66,36,39,
%U A117623 -72,37,40,-71,41,43,-83,44,45,-87,46,47,-91,50,-48,52,51,-100,53,54,-105,55,56,-110,59,58,-115,60
%N A117623 Values of k associated with A117622.
%C A117623 Does every positive number appear as an absolute value?
%t A117623 f[s_] := Block[{k = 1, d = Abs[Most@s - Rest@s], l = Last@s}, While[ PrimeQ[k] || MemberQ[s, k] || MemberQ[d, Abs[l - k]], k++ ]; Append[s, k]]; t = Nest[f, {1}, 71]; Rest@t - Most@t (* _Robert G. Wilson v_, Jun 13 2006 *)
%K A117623 sign
%O A117623 1,1
%A A117623 _Amarnath Murthy_, Apr 08 2006
%E A117623 More terms from _Jonathan Vos Post_, Apr 10 2006
%E A117623 Corrected and extended by _Robert G. Wilson v_, Jun 13 2006