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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 pair does not exist. 0
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..87.

Omar E. Pol, Illustration of the divisors of the first 12 positive integers

Index entries for sequences related to sigma(n)

EXAMPLE

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 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 triangle is [13, 8, 7].

CROSSREFS

Row sums give A000203.

Row lengths give A038548.

Right border gives A207376.

Column 1 is A065475.

Cf. A027750, A210959, A228814.

Sequence in context: A239639 A099816 A237273 * A262411 A280488 A250072

Adjacent sequences:  A272022 A272023 A272024 * A272026 A272027 A272028

KEYWORD

nonn,tabf

AUTHOR

Omar E. Pol, Apr 21 2016

STATUS

approved

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Last modified July 23 11:44 EDT 2019. Contains 325254 sequences. (Running on oeis4.)