A047823 Becomes prime after exactly 4 iterations of f(x) = sum of prime factors of x.

62, 69, 124, 133, 190, 194, 201, 206, 207, 213, 217, 219, 226, 235, 238, 248, 249, 254, 282, 286, 303, 309, 310, 314, 355, 380, 386, 388, 406, 411, 412, 426, 447, 451, 452, 458, 469, 476, 483, 489, 496, 505, 508, 553, 564, 572, 598, 602, 603, 606, 620, 621

Offset

1,1

Comments

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

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Mathematica

p4iQ[n_]:=PrimeQ[NestList[Total[Transpose[FactorInteger[#]][[1]]]&, n, 4]] == {False, False, False, False, True}; Select[Range[700], p4iQ] (* Harvey P. Dale, Aug 18 2013 *)

Crossrefs

Sequence in context: A024804 A025340 A048127 * A294738 A044997 A138172

Adjacent sequences: A047820 A047821 A047822 * A047824 A047825 A047826

Keyword

nonn

Author

David W. Wilson

Status

approved