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 A189561 #6 Mar 30 2012 17:22:58 %S A189561 1,3,7,9,13,13,16,18,19,24,17,26,17,23,25,23,28,25,23,37,21,28,25,22, %T A189561 36,30,34,38,28,28,27,28,45,37,35,36,34,35,33,33,31,35,35,31,43,33,37, %U A189561 44,36,37,38,30,50,36,44,47,43,33,43,50,36,39,38,31,41,48 %N A189561 Number of even numbers k that have n solutions to the equation x' = k, where x' denotes the arithmetic derivative (A003415). %C A189561 A189562 lists the even numbers for each n. %D A189561 See A003415. %H A189561 T. D. Noe, <a href="/A189561/b189561.txt">Table of n, a(n) for n = 0..250</a> %F A189561 a(n) is the number of k such that A099302(k) = n. %Y A189561 Cf. A003415, A099302, A189562. %K A189561 nonn %O A189561 0,2 %A A189561 _T. D. Noe_, Apr 24 2011