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 A225387 #9 May 17 2013 17:35:25 %S A225387 4,5,7,8,10,12,13,14,15,16,17,19,21,22,23,24,25,27,28,29,30,31,32,33, %T A225387 34,35,37,39,40,41,42,43,44,45,46,47,49,50,51,52,53,54,55,56,57,58,59, %U A225387 60,62,63,65,66,67,68,69,70,71,72,73,74,76,77,78,79,80,81,82,83,84,85,86 %N A225387 Construct sequences P,Q,R by the rules: Q = first differences of P, R = second differences of P, P starts with 1,3,9, Q starts with 2,6, R starts with 4; at each stage the smallest number not yet present in P,Q,R is appended to R. Sequence gives R. %C A225387 In contrast to A225376-A225378, here it is not required (and not true) that each number should appear just once in P union Q union R. On the other hand, again in contrast to A225376-A225378, here it is obvious that P, Q, R are infinite. %C A225387 The first three numbers that are repeated are 284, 2074, 3500, which appear in both P and Q. There may be no others. Of course R is disjoint from P and Q, by definition. %p A225387 See A225385. %Y A225387 Cf. A225385, A225386, A005228, A030124, A037257, A225376, A225377, A225378. %K A225387 nonn %O A225387 1,1 %A A225387 _N. J. A. Sloane_, May 15 2013