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 A078107 #15 May 29 2024 13:48:43 %S A078107 1,2,3,4,5,6,7,8,9,10,11,12,13,14,18,19,20,21,22,24 %N A078107 Numbers k such that it is not possible to arrange the numbers from 1 to k in a chain with adjacent links summing to a square. %C A078107 It seems certain, on account of the valences of the underlying graph, that necklaces exist for all larger k, but this may not yet have been proved. %C A078107 The problem originated (for k = 15) with Bernardo Recamán Santos of Colombia. The problem for necklaces is due to Joe Kisenwether. %C A078107 _Ed Pegg Jr_ and _W. Edwin Clark_ have found necklaces (and hence chains) for k = 32 onwards up to 50 and for several larger numbers. %C A078107 It has been proven that there are no more terms. See A090461 for details. - _Paolo Xausa_, May 29 2024 %e A078107 E.g., for 15, 16 or 17, use (16-)9-7-2-14-11-5-4-12-13-3-6-10-15-1-8(-17). %Y A078107 Cf. A071983, A071984, A090460, A090461. %K A078107 nonn,fini,full %O A078107 1,2 %A A078107 _R. K. Guy_, Dec 06 2002