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A047824 Becomes prime after exactly 5 iterations of f(x) = sum of prime factors of x. 0
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 (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..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

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Last modified September 29 06:25 EDT 2022. Contains 357082 sequences. (Running on oeis4.)