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

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

Offset

1,1

Links

Michael S. Branicky, Table of n, a(n) for n = 1..1400

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
print([a(n) for n in range(1, 82)]) # Michael S. Branicky, Dec 10 2021

Crossrefs

Cf. A034690, A086793.

Sequence in context: A140267 A343530 A262965 * A307166 A297910 A298503

Adjacent sequences: A094447 A094448 A094449 * A094451 A094452 A094453

Keyword

base,nonn

Author

Jason Earls, Jun 04 2004

Status

approved