A368216 - OEIS

A368216

Number of divisors of n that are antiharmonic numbers (A020487).

1, 1, 1, 2, 1, 1, 1, 2, 2, 1, 1, 2, 1, 1, 1, 3, 1, 2, 1, 3, 1, 1, 1, 2, 2, 1, 2, 2, 1, 1, 1, 3, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1, 2, 2, 1, 1, 3, 2, 3, 1, 2, 1, 2, 1, 2, 1, 1, 1, 3, 1, 1, 2, 4, 1, 1, 1, 2, 1, 1, 1, 4, 1, 1, 2, 2, 1, 1, 1, 4, 3, 1, 1, 2, 1, 1, 1, 2

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

OFFSET

1,4

COMMENTS

Differs from A046951 for n = 20, 40, 50, 60, 80, ....

LINKS

Table of n, a(n) for n=1..88.

FORMULA

a(p^k) = floor((k + 2)/2), p prime, k >= 1.

a(p*q) = 1, for p, q prime, p <> q.

a(A005117(k)) = 1, k >= 1.

Asymptotic mean: Limit_{m->oo} (1/m) * Sum_{k=1..m} a(k) = Sum_{k>=1} 1/A020487(k) = 1.784... . - Amiram Eldar, Jan 26 2024