A340792 -id:A340792 - cp's OEIS frontend

A340791 Irregular triangle read by rows in which row n lists the positive divisors of n that are >= sqrt(n) in decreasing order.

1, 2, 3, 4, 2, 5, 6, 3, 7, 8, 4, 9, 3, 10, 5, 11, 12, 6, 4, 13, 14, 7, 15, 5, 16, 8, 4, 17, 18, 9, 6, 19, 20, 10, 5, 21, 7, 22, 11, 23, 24, 12, 8, 6, 25, 5, 26, 13, 27, 9, 28, 14, 7, 29, 30, 15, 10, 6, 31, 32, 16, 8, 33, 11, 34, 17, 35, 7, 36, 18, 12, 9, 6, 37, 38, 19

Offset: 1

Charles Kusniec, Jan 21 2021

Reversing rows gives A161908.

			Triangle begins:
   1
   2
   3
   4  2
   5
   6  3
   7
   8  4
   9  3
  10  5
  11
  12  6  4
  13
  14  7
  15  5
  16  8  4
  17
  18  9  6
  19
  20 10  5
  21  7
  22 11
  23
  24 12  8  6

Cf. A038548 (row widths), A160180 (second column), A161908 (rows reversed), A340792.

row(n) = Vecrev(select(x->(x>=sqrt(n)), divisors(n))); \\ Michel Marcus, Jan 22 2021

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

Original entry on oeis.org

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

Charles Kusniec, Feb 27 2021

Reversing rows gives A161906.

			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

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

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

a(n) * A161908(n) = A340792(n)
A161906(n) * A340791(n) = A340792(n)
A027750(n) * A056538(n) = A061017(n)

More terms from Jinyuan Wang, Mar 13 2021

cp's OEIS Frontend

A340791 Irregular triangle read by rows in which row n lists the positive divisors of n that are >= sqrt(n) in decreasing order.

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