OFFSET
1,1
COMMENTS
f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.
MATHEMATICA
i2Q[n_]:=PrimeQ[NestList[Total[Transpose[FactorInteger[#]][[1]]]&, n, 2]] == {False, False, True}; Select[Range[200], i2Q] (* Harvey P. Dale, Jul 14 2012 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved