A047826 Becomes prime after exactly 7 iterations of f(x) = sum of prime factors of x.

1774, 2566, 3548, 4497, 5132, 6382, 6843, 7096, 7538, 8043, 8882, 8902, 9003, 9286, 10264, 10334, 10862, 10997, 11019, 11162, 11469, 11490, 12009, 12226, 12442, 12507, 12764, 12817, 12842, 13215, 13491, 13849, 13947, 14192, 14642, 14677

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..10000

Mathematica

spf7Q[n_]:=Boole[PrimeQ[NestList[Total[FactorInteger[#][[;; , 1]]]&, n, 7]]]=={0, 0, 0, 0, 0, 0, 0, 1}; Select[Range[15000], spf7Q] (* Harvey P. Dale, Dec 15 2025 *)

Crossrefs

Sequence in context: A176478 A187132 A185836 * A143995 A205938 A238307

Adjacent sequences: A047823 A047824 A047825 * A047827 A047828 A047829

Keyword

nonn

Author

David W. Wilson

Status

approved