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 A336580 #10 Jul 30 2020 00:31:06 %S A336580 1,2,3,4,5,6,7,8,9,12,15,24,25,35,36,45,48,72,75,125,135,140,144,175, %T A336580 216,225,250,270,280,288,375,384,432,540,625,675,864,875,1080,1125, %U A336580 1250,1296,1350,1575,1620,1680,1728,1750,1800,1875,1944,2160,2250,2500 %N A336580 Numbers k such that A334676(k) = 1. %C A336580 All terms are 7-smooth (A002473). %C A336580 This sequence is infinite as it contains the powers of 5. %H A336580 Rémy Sigrist, <a href="/A336580/b336580.txt">Table of n, a(n) for n = 1..10000</a> %H A336580 Rémy Sigrist, <a href="/A336580/a336580.png">Illustration of terms < 1000</a> %H A336580 Rémy Sigrist, <a href="/A336580/a336580.gp.txt">PARI program for A336580</a> %e A336580 Regarding the number 540: %e A336580 - 540 / 4 = 135, %e A336580 - 135 / 3 = 45, %e A336580 - 45 / 5 = 9, %e A336580 - 9 / 9 = 1, %e A336580 - so A334676(540) = 1 %e A336580 - and 540 belongs to this sequence. %o A336580 (PARI) for (n=1, #keep=vector(2500, n, n==1), if (keep[n], print1 (n ", "); for (d=2, min(9, #keep\n), if (setsearch (Set(digits(nd=n*d)), d), keep[nd]=1)))) %o A336580 (PARI) See Links section. %Y A336580 Cf. A000351, A002473, A334676. %K A336580 nonn,base %O A336580 1,2 %A A336580 _Rémy Sigrist_, Jul 26 2020