

A094450


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


1



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, 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, 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
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


LINKS



MATHEMATICA

Table[Length[NestWhileList[Total[Flatten[IntegerDigits/@Divisors[#]]]&, 10^n, #!= 15&]]1, {n, 90}] (* Harvey P. Dale, Mar 05 2019 *)


PROG

(Python)
from sympy import divisors
def sd(n): return sum(map(int, str(n)))
def f(n): return sum(sd(d) for d in divisors(n, generator=True))
def a(n):
i, c = 10**n, 0
while i != 15: i = f(i); c += 1
return c


CROSSREFS



KEYWORD

base,nonn


AUTHOR



STATUS

approved



