A387463 Total number of 3's in the decimal digits of the divisors of n.

0, 0, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 0, 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 0, 0, 2, 1, 1, 3, 1, 1, 2, 1, 1, 3, 0, 0, 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0, 1, 0, 0, 2, 0, 1, 2, 1, 1, 3, 0, 1, 2, 1, 0, 2, 1, 1, 1, 1, 0, 3, 0, 0, 1, 0, 1, 1, 0, 1, 1, 0, 0, 2, 1, 1, 3, 0, 0, 2, 0, 0, 3

Offset

1,30

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Example

a(33) = 3 because among the divisors of 33, 3 has one 3 and 33 has two, for a total of 3.

Maple

f:= proc(n) local t; add(subs(x=1, t)^3, t = expand((1+x+x^2)^n)) end proc:
map(f, [$1..100]);

Mathematica

a[n_]:=Count[Flatten[IntegerDigits/@Divisors[n]], 3]; Array[a, 99] (* James C. McMahon, Aug 30 2025 *)

Prog

(Python)
from sympy import divisors
def a(n): return sum(str(d).count("3") for d in divisors(n, generator=True))
print([a(n) for n in range(1, 100)]) # Michael S. Branicky, Aug 29 2025

Crossrefs

Cf. A385494, A387394, A387464.

Sequence in context: A124032 A382961 A254046 * A394352 A137457 A396505

Adjacent sequences: A387460 A387461 A387462 * A387464 A387465 A387466

Keyword

nonn

Author

Robert Israel, Aug 29 2025

Status

approved