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A048130
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Becomes prime or 4 after exactly 8 iterations of f(x) = sum of prime factors of x.
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2
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1257, 1556, 1774, 1982, 2566, 2649, 4249, 4405, 4497, 4645, 5086, 5169, 5286, 5317, 5462, 5574, 6070, 6074, 6382, 6518, 7064, 7149, 7197, 7284, 7694, 7813, 7947, 8043, 8193, 8593, 8605, 8852, 8894, 8902, 8998, 9057, 9182, 9562, 9575, 10232, 10326
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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 with multiplicity, so that f(1500) = 2+2+3+5+5+5 = 22.
Getting 4 is rare (only 1 such instance in the first 5,000 terms). - Harvey P. Dale, Nov 19 2023
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LINKS
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MATHEMATICA
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fi[n_]:=Total[Flatten[Table[#[[1]], #[[2]]]&/@FactorInteger[n]]]; bpQ[n_]:=Boole[PrimeQ[NestList[ fi[#]&, n, 8]]] =={0, 0, 0, 0, 0, 0, 0, 0, 1}||Nest[fi[#]&, n, 7]==4; Select[Range[11000], bpQ] (* Harvey P. Dale, Nov 19 2023 *)
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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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