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A047822 Becomes prime after exactly 3 iterations of f(x) = sum of prime factors of x. 0
26, 33, 38, 52, 70, 74, 76, 86, 99, 104, 105, 106, 115, 122, 129, 138, 140, 146, 148, 152, 159, 161, 166, 172, 178, 185, 187, 195, 205, 208, 209, 212, 218, 221, 222, 230, 231, 244, 246, 266, 267, 276, 278, 280, 292, 296, 297, 302, 304, 305, 315, 321, 327 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

f(x) = sum of prime factors without multiplicity, so that f(1500) = 2+3+5 = 10.

LINKS

Table of n, a(n) for n=1..53.

MATHEMATICA

aQ[n_] := Length[NestWhileList[Plus @@ First /@ FactorInteger[#] &, n, ! PrimeQ[#] &]] == 4; Select[Range[2, 330], aQ] (* Jayanta Basu, Aug 10 2013 *)

CROSSREFS

Sequence in context: A177210 A050770 A050438 * A048126 A080932 A129914

Adjacent sequences: A047819 A047820 A047821 * A047823 A047824 A047825

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified December 1 21:08 EST 2022. Contains 358476 sequences. (Running on oeis4.)