A304254 Irregular triangle read by rows: row n lists divisors of n^2 in decreasing order.

1, 4, 2, 1, 9, 3, 1, 16, 8, 4, 2, 1, 25, 5, 1, 36, 18, 12, 9, 6, 4, 3, 2, 1, 49, 7, 1, 64, 32, 16, 8, 4, 2, 1, 81, 27, 9, 3, 1, 100, 50, 25, 20, 10, 5, 4, 2, 1, 121, 11, 1, 144, 72, 48, 36, 24, 18, 16, 12, 9, 8, 6, 4, 3, 2, 1, 169, 13, 1, 196, 98, 49, 28, 14, 7, 4, 2, 1

Offset: 1

Author

Kritsada Moomuang, May 09 2018

Keywords

• nonn
• tabf

Examples

			Triangle begins:
  1;
  4, 2, 1;
  9, 3, 1;
  16, 8, 4, 2, 1;
  25, 5, 1;
  36, 18, 12, 9, 6, 4, 3, 2, 1;
  49, 7, 1;
  64, 32, 16, 8, 4, 2, 1;
  81, 27, 9, 3, 1;
  100, 50, 25, 20, 10, 5, 4, 2, 1;
  121, 11, 1;
  144, 72, 48, 36, 24, 18, 16, 12, 9, 8, 6, 4, 3, 2, 1;
  169, 13, 1;
  196, 98, 49, 28, 14, 7, 4, 2, 1;
  225, 75, 45, 25, 15, 9, 5, 3, 1;
  256, 128, 64, 32, 16, 8, 4, 2, 1;
  289, 17, 1;
  324, 162, 108, 81, 54, 36, 27, 18, 12, 9, 6, 4, 3, 2, 1;
  361, 19, 1;
  400, 200, 100, 80, 50, 40, 25, 20, 16, 10, 8, 5, 4, 2, 1;
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..11958 (rows 1..600 flattened)

Crossrefs

Cf. A048691 (row lengths), A065764 (row sums), A056538.

Programs

Mathematica

Table[Reverse[Divisors[n^2]], {n, 1, 14}] // Flatten (* Amiram Eldar, May 02 2025 *)

PARI

row(n) = Vecrev(divisors(n^2)); \\ Amiram Eldar, May 02 2025