OFFSET
1,1
COMMENTS
f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
MATHEMATICA
p4iQ[n_]:=PrimeQ[NestList[Total[Transpose[FactorInteger[#]][[1]]]&, n, 4]] == {False, False, False, False, True}; Select[Range[700], p4iQ] (* Harvey P. Dale, Aug 18 2013 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved