A174843 Irregular triangle in which row n lists the divisors of prime(n)-1.

1, 1, 2, 1, 2, 4, 1, 2, 3, 6, 1, 2, 5, 10, 1, 2, 3, 4, 6, 12, 1, 2, 4, 8, 16, 1, 2, 3, 6, 9, 18, 1, 2, 11, 22, 1, 2, 4, 7, 14, 28, 1, 2, 3, 5, 6, 10, 15, 30, 1, 2, 3, 4, 6, 9, 12, 18, 36, 1, 2, 4, 5, 8, 10, 20, 40, 1, 2, 3, 6, 7, 14, 21, 42, 1, 2, 23, 46, 1, 2, 4, 13, 26, 52, 1, 2, 29, 58, 1, 2, 3, 4

Offset: 1

Author

T. D. Noe, Mar 30 2010

Keywords

• nonn
• tabf

Comments

Row n begins with 1, ends with prime(n)-1, and has A008328(n) terms.

Examples

			The first 10 rows:
  1
  1, 2
  1, 2, 4
  1, 2, 3, 6
  1, 2, 5, 10
  1, 2, 3, 4, 6, 12
  1, 2, 4, 8, 16
  1, 2, 3, 6, 9, 18
  1, 2, 11, 22
  1, 2, 4, 7, 14, 28
		

Links

• T. D. Noe, Rows n=1..500 of triangle, flattened

Crossrefs

Cf. A008328 (row lengths), A008332 (row sums).

Programs

Mathematica

Flatten[Table[Divisors[p-1], {p, Prime[Range[100]]}]]

PARI

row(n) = divisors(prime(n)-1); \\ Amiram Eldar, May 02 2025