A351612 Number of ordered pairs, (s,t), 1 <= s <= t, such that (t^s) | n.

1, 2, 2, 4, 2, 4, 2, 5, 4, 4, 2, 7, 2, 4, 4, 7, 2, 7, 2, 7, 4, 4, 2, 9, 4, 4, 6, 7, 2, 8, 2, 8, 4, 4, 4, 12, 2, 4, 4, 9, 2, 8, 2, 7, 7, 4, 2, 12, 4, 7, 4, 7, 2, 10, 4, 9, 4, 4, 2, 13, 2, 4, 7, 11, 4, 8, 2, 7, 4, 8, 2, 15, 2, 4, 7, 7, 4, 8, 2, 12, 8, 4, 2, 13, 4, 4, 4, 9, 2, 13

Offset

1,2

Links

Table of n, a(n) for n=1..90.

Formula

a(n) = Sum_{(t^s)|n, 1<=s<=t<=n} 1.

Example

a(9) = 4; The ordered pairs are (1,1), (1,3), (1,9), (2,3).
a(36) = 12; The ordered pairs are (1,1), (1,2), (1,3), (1,4), (1,6), (1,9), (1,12), (1,18), (1,36), (2,2), (2,3), (2,6).

Crossrefs

Sequence in context: A001223 A118776 A249867 * A092520 A372714 A147848

Adjacent sequences: A351609 A351610 A351611 * A351613 A351614 A351615

Keyword

nonn

Author

Wesley Ivan Hurt, Feb 14 2022

Status

approved