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A168239 Iterate the map n -> sum of largest digit of all divisors of n; sequence gives number of steps to reach 14. 3
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified December 9 23:05 EST 2022. Contains 358710 sequences. (Running on oeis4.)