A048130 Becomes prime or 4 after exactly 8 iterations of f(x) = sum of prime factors of x.

1257, 1556, 1774, 1982, 2566, 2649, 4249, 4405, 4497, 4645, 5086, 5169, 5286, 5317, 5462, 5574, 6070, 6074, 6382, 6518, 7064, 7149, 7197, 7284, 7694, 7813, 7947, 8043, 8193, 8593, 8605, 8852, 8894, 8902, 8998, 9057, 9182, 9562, 9575, 10232, 10326

Offset

1,1

Comments

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

Getting 4 is rare (only 1 such instance in the first 5,000 terms). - Harvey P. Dale, Nov 19 2023

Links

Harvey P. Dale, Table of n, a(n) for n = 1..5000

Mathematica

fi[n_]:=Total[Flatten[Table[#[[1]], #[[2]]]&/@FactorInteger[n]]]; bpQ[n_]:=Boole[PrimeQ[NestList[ fi[#]&, n, 8]]] =={0, 0, 0, 0, 0, 0, 0, 0, 1}||Nest[fi[#]&, n, 7]==4; Select[Range[11000], bpQ] (* Harvey P. Dale, Nov 19 2023 *)

Crossrefs

Sequence in context: A304829 A216941 A159726 * A256652 A211773 A215991

Adjacent sequences: A048127 A048128 A048129 * A048131 A048132 A048133

Keyword

nonn

Author

David W. Wilson

Status

approved