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

1,2

Links

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

Example

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;

Mathematica

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

Prog

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

Crossrefs

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

Sequence in context: A397528 A016505 A383266 * A010310 A021241 A016691

Adjacent sequences: A304251 A304252 A304253 * A304255 A304256 A304257

Keyword

nonn,tabf

Author

Kritsada Moomuang, May 09 2018

Status

approved