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A085790 Integers sorted by the sum of their divisors. 9
1, 2, 3, 5, 4, 7, 6, 11, 9, 13, 8, 10, 17, 19, 14, 15, 23, 12, 29, 16, 25, 21, 31, 22, 37, 18, 27, 20, 26, 41, 43, 33, 35, 47, 34, 53, 28, 39, 49, 24, 38, 59, 61, 32, 67, 30, 46, 51, 55, 71, 73, 45, 57, 79, 44, 65, 83, 40, 58, 89, 36, 50, 42, 62, 69, 77, 52, 97, 101, 63, 103, 85 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Integers having the same sum of divisors are sorted in ascending order, e.g., sigma(14)=sigma(15)=sigma(23)=24 -> a(15)=14, a(16)=15, a(17)=23.

Also an irregular triangle where the k-th row consists of all numbers with divisor sum k. See A054973(k) for the k-th row length. - Jeppe Stig Nielsen, Jan 29 2015

LINKS

Hugo Pfoertner, Table of n, a(n) for n=1..10000

Jeppe Stig Nielsen, First 10000 rows of the triangle for a(n)

EXAMPLE

a(9)=9, a(10)=13, a(11)=8 because sigma(9)=13=9+3+1, sigma(13)=14=13+1,

sigma(8)=15=8+4+2+1 and there are no other numbers with those sigma values.

Irregular triangle starts (row numbers to the left of colons are not part of this sequence):

1: 1,

2:

3: 2,

4: 3,

5:

6: 5,

7: 4,

8: 7,

9:

10:

11:

12: 6, 11,

13: 9,

14: 13,

15: 8,

16:

17:

18: 10, 17,

19:

20: 19,

21:

22:

23:

24: 14, 15, 23,

25:

- Jeppe Stig Nielsen, Feb 02 2015

CROSSREFS

Cf. A000203 (sigma(n)), A007609 (values taken by sigma(n), sorted), A002191 (possible values for sigma(n)), A002192 (first column).

Cf. A152454 (similar sequence for proper divisors only (aliquot parts)).

Sequence in context: A282649 A102454 A232640 * A257339 A210882 A117120

Adjacent sequences:  A085787 A085788 A085789 * A085791 A085792 A085793

KEYWORD

easy,nonn,tabf

AUTHOR

Hugo Pfoertner, Jul 23 2003

STATUS

approved

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Last modified February 20 16:25 EST 2018. Contains 299380 sequences. (Running on oeis4.)