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A094450 Number of iterations of the sum of digits of the divisors of 10^n needed to reach 15.

%I A094450 #10 Dec 10 2021 07:25:10
%S A094450 12,10,16,15,3,11,4,13,6,6,5,19,16,3,11,13,19,7,5,9,6,16,16,19,5,3,12,
%T A094450 3,18,16,4,10,6,16,18,12,4,16,12,13,12,5,12,5,20,15,16,12,4,16,4,20,5,
%U A094450 19,4,6,21,5,6,5,21,12,5,16,13,17,6,5,7,21,20,18,12,10,6,18,13,13,6,13,15
%N A094450 Number of iterations of the sum of digits of the divisors of 10^n needed to reach 15.
%H A094450 Michael S. Branicky, <a href="/A094450/b094450.txt">Table of n, a(n) for n = 1..1400</a>
%t A094450 Table[Length[NestWhileList[Total[Flatten[IntegerDigits/@Divisors[#]]]&,10^n, #!= 15&]]-1,{n,90}] (* _Harvey P. Dale_, Mar 05 2019 *)
%o A094450 (Python)
%o A094450 from sympy import divisors
%o A094450 def sd(n): return sum(map(int, str(n)))
%o A094450 def f(n): return sum(sd(d) for d in divisors(n, generator=True))
%o A094450 def a(n):
%o A094450     i, c = 10**n, 0
%o A094450     while i != 15: i = f(i); c += 1
%o A094450     return c
%o A094450 print([a(n) for n in range(1, 82)]) # _Michael S. Branicky_, Dec 10 2021
%Y A094450 Cf. A034690, A086793.
%K A094450 base,nonn
%O A094450 1,1
%A A094450 _Jason Earls_, Jun 04 2004