A319135 Irregular triangle read by rows in which row n lists the positive divisors of n that are <= sqrt(n) in decreasing order.

1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 3, 1, 2, 1, 1, 3, 2, 1, 1, 2, 1, 3, 1, 4, 2, 1, 1, 3, 2, 1, 1, 4, 2, 1, 3, 1, 2, 1, 1, 4, 3, 2, 1, 5, 1, 2, 1, 3, 1, 4, 2, 1, 1, 5, 3, 2, 1, 1, 4, 2, 1, 3, 1, 2, 1, 5, 1, 6, 4, 3, 2, 1, 1, 2, 1, 3, 1, 5, 4, 2, 1, 1, 6, 3, 2, 1

Offset

1,4

Comments

Reversing rows gives A161906.

Links

Table of n, a(n) for n=1..87.

Formula

a(n) * A161908(n) = A340792(n)

A161906(n) * A340791(n) = A340792(n)

A027750(n) * A056538(n) = A061017(n)

Example

Triangle begins:
1
1
1
2 1
1
2 1
1
2 1
3 1
2 1
1
3 2 1
1
2 1
3 1
4 2 1

Prog

(PARI) row(n) = Vecrev(select(x->(x<=sqrt(n)), divisors(n))); \\ Jinyuan Wang, Mar 13 2021

Crossrefs

Cf. A038548 (row widths), A033676 (first column), A333750 (second column), A161906 (rows reversed), A027750, A056538, A061017, A340791, A340792.

Sequence in context: A254434 A076845 A161906 * A338884 A204901 A016014

Adjacent sequences: A319132 A319133 A319134 * A319136 A319137 A319138

Keyword

nonn,tabf

Author

Charles Kusniec, Feb 27 2021

Extensions

More terms from Jinyuan Wang, Mar 13 2021

Status

approved