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 A081758 #10 May 31 2025 15:24:41
%S A081758 2,3,4,5,5,7,5,5,7,11,7,13,6,6,6,17,6,19,6,7,13,23,6,7,8,6,11,29,7,31,
%T A081758 7,9,19,7,7,37,10,8,11,41,7,43,8,11,10,47,11,9,7,9,17,53,11,8,13,13,
%U A081758 31,59,7,61,14,13,7,8,8,67,10,15,9,71,7,73,16,13,23,8,8,79,13,7,43,83,9,13,11
%N A081758 Sum of prime factors (with repetition) of sum of prime factors (with repetition) of n.
%C A081758 a(n) = A001414(A001414(n)). For further iterations see: A029908, A002217;
%C A081758 a(n)=n iff n is prime or 4.
%H A081758 Harvey P. Dale, <a href="/A081758/b081758.txt">Table of n, a(n) for n = 2..1000</a>
%e A081758 18 = 2*3*3 -> 2+3+3 = 2*2*2 -> 2+2+2 = 6: a(18) = 6.
%t A081758 spf[n_]:=Flatten[Table[#[[1]],#[[2]]]&/@FactorInteger[n]]; Table[Nest[Total[spf[#]]&,n,2],{n,2,90}] (* _Harvey P. Dale_, May 31 2025 *)
%K A081758 nonn
%O A081758 2,1
%A A081758 _Reinhard Zumkeller_, Apr 08 2003