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A047823
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Becomes prime after exactly 4 iterations of f(x) = sum of prime factors of x.
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1
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62, 69, 124, 133, 190, 194, 201, 206, 207, 213, 217, 219, 226, 235, 238, 248, 249, 254, 282, 286, 303, 309, 310, 314, 355, 380, 386, 388, 406, 411, 412, 426, 447, 451, 452, 458, 469, 476, 483, 489, 496, 505, 508, 553, 564, 572, 598, 602, 603, 606, 620, 621
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OFFSET
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1,1
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COMMENTS
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f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.
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LINKS
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MATHEMATICA
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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 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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