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 A359535 #31 Jan 25 2023 10:19:51 %S A359535 1,2,4,6,3,8,5,12,7,10,13,15,14,16,18,20,9,22,11,28,17,91,19,25,33,21, %T A359535 29,39,34,23,32,38,51,57,24,37,40,26,42,30,43,69,46,27,47,58,87,31,35, %U A359535 44,52,54,36,74,41,59,50,60,86,48,62,93,45,65,94,49,63,53,70,72,55,82,56,1591 %N A359535 Lexicographically earliest sequence of distinct positive integers such that a(a(n)) and a(a(n+1)) share a common factor when n >= 2. %C A359535 The common factor rule does not apply at n=1 so the sequence starts with a(1) = 1 and a(2) = 2. %H A359535 Samuel Harkness, <a href="/A359535/b359535.txt">Table of n, a(n) for n = 1..10000</a> %H A359535 Samuel Harkness, <a href="/A359535/a359535.m.txt">MATLAB program</a> %e A359535 a(3) cannot be 3 since then a(a(2))=2 and a(a(3))=3 would have no common factor, but a(3) = 4 is allowed (and puts a constraint on the subsequent a(4) value). %e A359535 a(6) is 8 because so far we have (1,2,4,6,3). We see that the 6th term must share a factor with the 4th and 3rd terms, which are 6 and 4, respectively. The smallest number not already used that satisfies this property is 8. %o A359535 (MATLAB) See Links section. %Y A359535 Cf. A064413. %K A359535 nonn %O A359535 1,2 %A A359535 _Neal Gersh Tolunsky_, Jan 04 2023