A047824 Becomes prime after exactly 5 iterations of f(x) = sum of prime factors of x.

134, 177, 262, 268, 398, 422, 466, 524, 531, 536, 573, 614, 669, 706, 742, 753, 796, 817, 818, 844, 849, 898, 915, 921, 932, 933, 934, 974, 1006, 1048, 1072, 1149, 1165, 1202, 1222, 1227, 1228, 1238, 1239, 1243, 1294, 1322, 1347, 1354, 1385, 1393, 1398

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..47.

Mathematica

p5iQ[n_]:=PrimeQ[NestList[Total[Transpose[FactorInteger[#]][[1]]]&, n, 5]] == {False, False, False, False, False, True}; Select[Range[2000], p5iQ] (* Harvey P. Dale, May 21 2015 *)

Crossrefs

Sequence in context: A252133 A255795 A048128 * A020353 A050963 A051387

Adjacent sequences: A047821 A047822 A047823 * A047825 A047826 A047827

Keyword

nonn

Author

David W. Wilson

Status

approved