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 A288921 #12 Jun 20 2017 23:53:04 %S A288921 1,1260,2,630,4,315,8,180,7,240,6,210,10,126,16,90,14,120,12,105,20, %T A288921 63,32,45,28,60,21,80,18,70,24,75,36,35,48,30,42,40,54,50,66,56,72,25, %U A288921 84,15,96,33,100,27,112,39,132,49,108,44,117,64,81,88,78,98,99 %N A288921 Lexicographically earliest sequence of distinct positive terms such that the product of two consecutive terms has at least 34 divisors. %C A288921 The number of divisors is given by A000005. %C A288921 This sequence is a permutation of the natural numbers, with inverse A288922. %C A288921 Conjecturally, a(n) ~ n. %C A288921 See also A288923 for similar sequences. %H A288921 Rémy Sigrist, <a href="/A288921/b288921.txt">Table of n, a(n) for n = 1..30000</a> %H A288921 Rémy Sigrist, <a href="/A288921/a288921.gp.txt">PARI program for A288921</a> %H A288921 <a href="/index/Per#IntegerPermutation">Index entries for sequences that are permutations of the natural numbers</a> %e A288921 The first terms, alongside a(n)*a(n+1) and its number of divisors, are: %e A288921 n a(n) a(n)*a(n+1) Number of divisors %e A288921 -- ---- ----------- ------------------ %e A288921 1 1 1260 36 %e A288921 2 1260 2520 48 %e A288921 3 2 1260 36 %e A288921 4 630 2520 48 %e A288921 5 4 1260 36 %e A288921 6 315 2520 48 %e A288921 7 8 1440 36 %e A288921 8 180 1260 36 %e A288921 9 7 1680 40 %e A288921 10 240 1440 36 %e A288921 11 6 1260 36 %e A288921 12 210 2100 36 %e A288921 13 10 1260 36 %e A288921 14 126 2016 36 %e A288921 15 16 1440 36 %e A288921 16 90 1260 36 %e A288921 17 14 1680 40 %e A288921 18 120 1440 36 %e A288921 19 12 1260 36 %e A288921 20 105 2100 36 %Y A288921 Cf. A000005, A288922 (inverse), A288923. %K A288921 nonn,look %O A288921 1,2 %A A288921 _Rémy Sigrist_, Jun 19 2017