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 A048131 #7 Sep 06 2021 19:34:32 %S A048131 4659,5294,5937,9286,10334,10843,15490,16382,17972,18201,18588,18735, %T A048131 19137,19984,20059,22482,23073,23806,25405,26405,26547,27622,27845, %U A048131 28694,28772,30062,30486,31686,32156,32313,33177,33238,33414,33944 %N A048131 Becomes prime or 4 after exactly 9 iterations of f(x) = sum of prime factors of x. %C A048131 f(x) = sum of prime factors with multiplicity, so that f(1500) = 2+2+3+5+5+5 = 22. %t A048131 sopf[n_]:=Total[Flatten[Table[#[[1]],#[[2]]]&/@FactorInteger[n]]]; nifQ[ n_]:=Length[NestWhileList[sopf,n,!PrimeQ[#]&&#!=4&]]==10; Select[ Range[ 4000,34000],nifQ] (* _Harvey P. Dale_, Sep 06 2021 *) %K A048131 nonn %O A048131 1,1 %A A048131 _David W. Wilson_