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A287262 Numbers whose sum of proper divisors is equal to 690100611194. 7
1258418761414, 1276686130498, 1286096593354, 1290188098942, 1306261870882, 1321049741038, 1338795185146, 1350625481098, 1359498202882, 1365723585502, 1367261834038, 1371277504834, 1372962401386, 1373062247098, 1373771709754, 1374112095298, 1374709701094 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The number 690100611194 is the 49th term of A283157. That is, no even number below it has more preimages under the sum-of-proper-divisors function. Up to 2^40, this is the even number with the greatest number of preimages. As of May 22 2017, this is the largest known even number with the greatest number of preimages.

There are exactly 139 terms in the sequence.

In 2016, C. Pomerance proved that, for every e > 0, the number of preimages is O_e(n^{2/3+e}).

Conjecture: there exists a positive real number k such that the number of preimages of an even number n is O((log n)^k).

LINKS

Anton Mosunov, Table of n, a(n) for n = 1..139

C. Pomerance, The first function and its iterates, A Celebration of the Work of R. L. Graham, S. Butler, J. Cooper, and G. Hurlbert, eds., Cambridge U. Press, to appear.

EXAMPLE

a(1) = 1258418761414, because it is the smallest number whose sum of proper divisors is equal to 690100611194: 1 + 2 + 31 + 62 + 20297076797 + 40594153594 + 629209380707 = 690100611194.

CROSSREFS

Cf. A001065, A283156, A283157, A287233, A287238, A287247, A287251.

Sequence in context: A060088 A077300 A083407 * A260250 A088280 A011526

Adjacent sequences:  A287259 A287260 A287261 * A287263 A287264 A287265

KEYWORD

fini,full,nonn

AUTHOR

Anton Mosunov, May 22 2017

STATUS

approved

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Last modified May 22 09:50 EDT 2022. Contains 353949 sequences. (Running on oeis4.)