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 A225386 #11 May 17 2013 17:35:03 %S A225386 2,6,11,18,26,36,48,61,75,90,106,123,142,163,185,208,232,257,284,312, %T A225386 341,371,402,434,467,501,536,573,612,652,693,735,778,822,867,913,960, %U A225386 1009,1059,1110,1162,1215,1269,1324,1380,1437,1495,1554,1614,1676,1739,1804,1870,1937,2005,2074,2144 %N A225386 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 Q. %C A225386 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 A225386 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 A225386 See A225385. %Y A225386 Cf. A225385, A225387, A005228, A030124, A037257, A225376, A225377, A225378. %K A225386 nonn %O A225386 1,1 %A A225386 _N. J. A. Sloane_, May 15 2013