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 A258849 #5 Jun 12 2015 20:41:51 %S A258849 0,0,0,0,4,0,4,4,12288,81920,0,0,278380544,4,4931584,278380544, %T A258849 14768867966976,4,128412352512,14768867966976,375877192068366336, %U A258849 14768867966976,14768867966976,375877192068366336 %N A258849 The n-th pi-based arithmetic derivative of n. %F A258849 a(n) = A258851^n(n) = A258850(n,n). %p A258849 with(numtheory): %p A258849 d:= n-> n*add(i[2]*pi(i[1])/i[1], i=ifactors(n)[2]): %p A258849 A:= proc(n, k) option remember; `if`(k=0, n, d(A(n, k-1))) end: %p A258849 a:= n-> A(n$2): %p A258849 seq(a(n), n=0..23); %Y A258849 Main diagonal of A258850. %Y A258849 Cf. A000720, A258851. %K A258849 nonn %O A258849 0,5 %A A258849 _Alois P. Heinz_, Jun 12 2015