A272025 Irregular triangle read by rows, n >= 1, 1 <= k <= A038548(n), in which T(n,k) is the sum of the k-th pair of conjugate divisors of n, or T(n,k) is the central divisor of n if such a pair does not exist.

1, 3, 4, 5, 2, 6, 7, 5, 8, 9, 6, 10, 3, 11, 7, 12, 13, 8, 7, 14, 15, 9, 16, 8, 17, 10, 4, 18, 19, 11, 9, 20, 21, 12, 9, 22, 10, 23, 13, 24, 25, 14, 11, 10, 26, 5, 27, 15, 28, 12, 29, 16, 11, 30, 31, 17, 13, 11, 32, 33, 18, 12, 34, 14, 35, 19, 36, 12, 37, 20, 15, 13, 6, 38, 39, 21, 40, 16, 41, 22, 14, 13, 42, 43, 23, 17, 13

Offset: 1

Author

Omar E. Pol, Apr 21 2016

Keywords

• nonn
• tabf

Examples

			Triangle begins:
  1;
  3;
  4;
  5, 2;
  6;
  7, 5;
  8;
  9, 6;
  10, 3;
  11, 7;
  12;
  13, 8, 7;
  ...
For n = 9 the divisors of 9 are [1, 3, 9]. There is only one pair of conjugate divisors: [1, 9], and the central divisor is 3, so the 9th row of the triangle is [10, 3].
For n = 12 the divisors of 12 are [1, 2, 3, 4, 6, 12]. There are three pairs of conjugate divisors, they are [1, 12], [2, 6], [3, 4], so the 12th row of the triangle is [13, 8, 7].
		

Links

• Omar E. Pol, Illustration of the divisors of the first 12 positive integers
• Index entries for sequences related to sigma(n)

Crossrefs

Row sums give A000203.

Row lengths give A038548.

Right border gives A207376.

Column 1 is A065475.

Cf. A027750, A210959, A228814.