A168239 - OEIS

%I #8 Feb 05 2022 11:31:00

%S 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,

%T 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,

%U 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

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

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

%H Harvey P. Dale, <a href="/A168239/b168239.txt">Table of n, a(n) for n = 2..1000</a>

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

%o (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

%Y Cf. A054055, A209928.

%K base,easy,nonn

%O 2,1

%A _Jason Earls_, Nov 21 2009