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

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

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