A048131 Becomes prime or 4 after exactly 9 iterations of f(x) = sum of prime factors of x.

4659, 5294, 5937, 9286, 10334, 10843, 15490, 16382, 17972, 18201, 18588, 18735, 19137, 19984, 20059, 22482, 23073, 23806, 25405, 26405, 26547, 27622, 27845, 28694, 28772, 30062, 30486, 31686, 32156, 32313, 33177, 33238, 33414, 33944

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Comments

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

Programs

Mathematica

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 *)