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A048128 Becomes prime or 4 after exactly 6 iterations of f(x) = sum of prime factors of x. 2
134, 177, 213, 262, 309, 334, 339, 398, 445, 469, 505, 514, 534, 606, 670, 723, 742, 753, 758, 763, 788, 793, 802, 804, 817, 818, 849, 865, 913, 914, 915, 926, 961, 976, 998, 1011, 1016, 1038, 1052, 1060, 1090, 1098, 1101, 1115, 1143, 1154, 1165, 1195 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

f(x) = sum of prime factors with multiplicity, so that f(1500) = 2+2+3+5+5+5 = 22.

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..3500

MATHEMATICA

nxt[n_]:=Total[Flatten[Table[#[[1]], {#[[2]]}]&/@FactorInteger[n]]]; sixiQ[ n_]:=Module[{c=NestList[nxt, n, 6]}, PrimeQ[c]=={False, False, False, False, False, False, True} || FirstPosition[ c, 4, 1] == {7}]; Select[ Range[ 1200], sixiQ] (* Harvey P. Dale, Oct 21 2014 *)

CROSSREFS

Sequence in context: A274132 A252133 A255795 * A047824 A020353 A050963

Adjacent sequences: A048125 A048126 A048127 * A048129 A048130 A048131

KEYWORD

nonn

AUTHOR

David W. Wilson

STATUS

approved

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Last modified November 27 13:59 EST 2022. Contains 358405 sequences. (Running on oeis4.)