The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A048130 Becomes prime or 4 after exactly 8 iterations of f(x) = sum of prime factors of x. 2
 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 (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. 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified August 4 23:59 EDT 2024. Contains 374934 sequences. (Running on oeis4.)