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 A189558 #18 Oct 08 2012 14:57:24 %S A189558 2,4,10,16,24,54,48,60,84,90,114,144,150,120,168,234,216,252,288,210, %T A189558 354,240,432,360,330,552,456,390,462,480,546,420,510,600,672,792,756, %U A189558 714,798,690,720,630,1116,1026,930,780,870,960,900,924,1134,1296,840 %N A189558 Least number k>0 such that x' = k has n solutions, where x' is the arithmetic derivative (A003415) of x. %C A189558 It appears that all terms are even. See A189559 for k restricted to prime numbers and A189560 restricted to odd numbers. %D A189558 See A003415. %H A189558 T. D. Noe and Donovan Johnson, <a href="/A189558/b189558.txt">Table of n, a(n) for n = 0..5000</a> (terms up to a(665) from T. D. Noe) %F A189558 a(n) is the least k>0 such that A099302(k) = n. %Y A189558 See A003415, A099302, A189559, A189560. %K A189558 nonn %O A189558 0,1 %A A189558 _T. D. Noe_, Apr 24 2011