A048131 - OEIS

%I #7 Sep 06 2021 19:34:32

%S 4659,5294,5937,9286,10334,10843,15490,16382,17972,18201,18588,18735,

%T 19137,19984,20059,22482,23073,23806,25405,26405,26547,27622,27845,

%U 28694,28772,30062,30486,31686,32156,32313,33177,33238,33414,33944

%N Becomes prime or 4 after exactly 9 iterations of f(x) = sum of prime factors of x.

%C f(x) = sum of prime factors with multiplicity, so that f(1500) = 2+2+3+5+5+5 = 22.

%t 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 nonn

%O 1,1

%A _David W. Wilson_