A387394 Total number of 2's in the decimal digits of the divisors of n.

0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 2, 0, 1, 0, 1, 0, 1, 0, 2, 1, 3, 1, 3, 1, 2, 1, 2, 1, 1, 0, 2, 0, 1, 0, 2, 0, 1, 0, 2, 0, 3, 0, 3, 0, 2, 0, 3, 0, 2, 0, 3, 0, 2, 0, 2, 0, 2, 0, 3, 0, 2, 1, 2, 0, 3, 0, 1, 1, 1, 0, 4, 0, 1, 1, 1, 0, 2, 0, 2, 1, 2, 0, 5, 0, 1, 1, 3, 0, 1, 0, 3, 0, 1, 0, 4, 0, 1, 0

Offset

1,12

Links

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

Example

a(22) = 3 because among the divisors of 22, 2 has one 2 and 22 has two, for a total of 3.

Maple

f:= proc(n) local d; add(numboccur(2, convert(d, base, 10)), d=numtheory:-divisors(n)) end proc:
map(f, [$1..200]);

Mathematica

a[n_]:=Count[IntegerDigits[Divisors[n]]//Flatten, 2]; Array[a, 99] (* Stefano Spezia, Aug 29 2025 *)

Prog

(PARI) a(n) = sumdiv(n, d, #select(x->(x==2), digits(d))); \\ Michel Marcus, Aug 28 2025
(Python)
from sympy import divisors
def a(n): return sum(str(d).count("2") 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, A387396, A387463.

Sequence in context: A292242 A280800 A083889 * A360079 A127523 A364389

Adjacent sequences: A387391 A387392 A387393 * A387395 A387396 A387397

Keyword

nonn,base

Author

Robert Israel, Aug 28 2025

Status

approved