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 A258847 #5 Jun 12 2015 20:39:47
%S A258847 0,1,2,4,6,10,13,20,21,33,54,86,146,339,788,2947,14870,94801,706961,
%T A258847 5566784,43958933,317950465,2406052444,19645433193,146175038733,
%U A258847 1479263447899,16135114175706,203382520812382,2606355260220040,32974597626726301,406609097787758227
%N A258847 Sum of the k-th pi-based arithmetic derivative of n-k for k=0..n.
%F A258847 a(n) = Sum_{k=0..n} A258850(n-k,k).
%p A258847 with(numtheory):
%p A258847 d:= n-> n*add(i[2]*pi(i[1])/i[1], i=ifactors(n)[2]):
%p A258847 A:= proc(n, k) option remember; `if`(k=0, n, d(A(n, k-1))) end:
%p A258847 a:= proc(n) option remember; add(A(h, n-h), h=0..n) end:
%p A258847 seq(a(n), n=0..30);
%Y A258847 Antidiagonal sums of A258850.
%Y A258847 Cf. A000720, A258851.
%K A258847 nonn
%O A258847 0,3
%A A258847 _Alois P. Heinz_, Jun 12 2015