A048128 Becomes prime or 4 after exactly 6 iterations of f(x) = sum of prime factors of x.

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

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