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 A368358 #13 Dec 31 2023 12:38:12 %S A368358 1,4,6,5,7,16,24,20,28,18,26,22,30,17,25,21,29,19,27,23,31,64,96,80, %T A368358 112,72,104,88,120,68,100,84,116,76,108,92,124,66,98,82,114,74,106,90, %U A368358 122,70,102,86,118,78,110,94,126,65,97,81,113,73,105,89,121,69,101,85,117,77,109 %N A368358 Consider the doubly-infinite permutation P defined on page 87 of Davis et al. (1977); sequence gives the terms starting at and to the left of 1, in reverse order. %C A368358 P is a doubly-infinite sequence which is a permutation of the positive integers and contains no increasing or decreasing 4-term arithmetic progression. %C A368358 A central portion of P, showing terms to the left (the present sequence) and right (A368357) of the central 1: %C A368358 ..., 18, 28, 20, 24, 16, 7, 5, 6, 4, 1, 2, 3, 8, 12, 10, 14, 9, 13, 11, 15, ... %C A368358 See the link for a larger portion. %H A368358 Davis, J. A.; Entringer, R. C.; Graham, R. L.; and Simmons, G. J.; <a href="http://matwbn.icm.edu.pl/ksiazki/aa/aa34/aa3417.pdf">On permutations containing no long arithmetic progressions</a>, Acta Arith. 34 (1977), no. 1, 81-90. The recurrence defining P is given in Fact 6 on page 87. %H A368358 N. J. A. Sloane, <a href="/A368357/a368357.txt">A portion of P showing 511 consecutive terms around 1</a> %H A368358 N. J. A. Sloane, <a href="/A368357/a368357_1.txt">Maple code</a> %Y A368358 Cf. A003407, A368357 (the right-hand portion). %K A368358 nonn %O A368358 0,2 %A A368358 _N. J. A. Sloane_, Dec 31 2023