A168239 Iterate the map n -> sum of largest digit of all divisors of n; sequence gives number of steps to reach 14.

6, 5, 4, 12, 11, 3, 2, 6, 7, 7, 10, 5, 0, 1, 7, 3, 9, 8, 2, 6, 12, 5, 13, 8, 11, 3, 12, 8, 12, 5, 14, 3, 1, 10, 14, 3, 3, 8, 4, 13, 9, 13, 1, 13, 11, 3, 2, 4, 9, 8, 7, 12, 14, 11, 5, 3, 3, 8, 5, 4, 11, 13, 13, 2, 14, 3, 12, 8, 15, 3, 6, 3, 4, 12, 6, 8, 4, 8, 14, 13, 2, 7, 9, 7, 2, 7, 13, 8, 4, 3, 9, 8

Offset

2,1

References

J. Earls, "Black Hole 14," Mathematical Bliss, Pleroma Publications, 2009, pages 18-22. ASIN: B002ACVZ6O

Links

Harvey P. Dale, Table of n, a(n) for n = 2..1000

Mathematica

nl[n_]:=NestWhileList[Total[Max[IntegerDigits[#]]&/@Divisors[ #]]&, n, #!= 14&]; Table[Length[nl[k]], {k, 2, 100}]-1 (* Harvey P. Dale, Feb 05 2022 *)

Prog

(PARI) a(n)=my(k); while(n!=14, n=sumdiv(n, d, vecmax(eval(Vec(Str(d))))); k++); k \\ Charles R Greathouse IV, May 22 2012

Crossrefs

Cf. A054055, A209928.

Sequence in context: A220086 A094773 A205651 * A291068 A019131 A019132

Adjacent sequences: A168236 A168237 A168238 * A168240 A168241 A168242

Keyword

base,easy,nonn

Author

Jason Earls, Nov 21 2009

Status

approved