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A047822 Becomes prime after exactly 3 iterations of f(x) = sum of prime factors of x. 0

%I

%S 26,33,38,52,70,74,76,86,99,104,105,106,115,122,129,138,140,146,148,

%T 152,159,161,166,172,178,185,187,195,205,208,209,212,218,221,222,230,

%U 231,244,246,266,267,276,278,280,292,296,297,302,304,305,315,321,327

%N Becomes prime after exactly 3 iterations of f(x) = sum of prime factors of x.

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

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

%K nonn

%O 1,1

%A _David W. Wilson_

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Last modified February 8 12:49 EST 2023. Contains 360138 sequences. (Running on oeis4.)