A358088 Number of pairs (s,t) with s and t squarefree, 1 <= s < t <= n and s | t.

0, 1, 2, 2, 3, 6, 7, 7, 7, 10, 11, 11, 12, 15, 18, 18, 19, 19, 20, 20, 23, 26, 27, 27, 27, 30, 30, 30, 31, 38, 39, 39, 42, 45, 48, 48, 49, 52, 55, 55, 56, 63, 64, 64, 64, 67, 68, 68, 68, 68, 71, 71, 72, 72, 75, 75, 78, 81, 82, 82, 83, 86, 86, 86, 89, 96, 97, 97, 100, 107, 108

Offset

1,3

Links

Table of n, a(n) for n=1..71.

Formula

a(n) = Sum_{i=1..n} Sum_{k=1..i-1} mu(i)^2 * mu(k)^2 * c(i/k), where c(n) = 1 - ceiling(n) + floor(n).

Example

a(9) = 7. The pairs are (1,2), (1,3), (1,5), (1,6), (1,7), (2,6) and (3,6).

Crossrefs

Sequence in context: A011961 A182713 A229626 * A091770 A032058 A241744

Adjacent sequences: A358085 A358086 A358087 * A358089 A358090 A358091

Keyword

nonn

Author

Wesley Ivan Hurt, Oct 30 2022

Status

approved