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A060678
Numbers k such that sigma (x) = k has exactly 11 solutions.
12
576, 1296, 2976, 3168, 3648, 3720, 4788, 4896, 5544, 6300, 9000, 9840, 10656, 11808, 12528, 13020, 13320, 14760, 15456, 16740, 17920, 18288, 18576, 19344, 19840, 20400, 21280, 22800, 23296, 24300, 26712, 26928, 27552, 27936, 28392
OFFSET
1,1
EXAMPLE
576 = sigma(210) = sigma(282) = sigma(310) = sigma(322) = sigma(345) = sigma(357) = sigma(382) = sigma(385) = sigma(497) = sigma(517) = sigma(527).
MATHEMATICA
a = Table[ 0, {30000} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 30001, a[ [ s ] ]++ ], {n, 1, 30000} ]; Select[ Range[ 30000 ], a[ [ # ] ] == 11 & ]
PROG
(PARI) is(k) = invsigmaNum(k) == 11 \\ Amiram Eldar, Nov 18 2024, using Max Alekseyev's invphi.gp
CROSSREFS
Cf. A000203.
Number of solutions: A007369 (0), A007370 (1), A007371 (2), A007372 (3), A060660 (4), A060661 (5), A060662 (6), A060663 (7), A060664 (8), A060665 (9), A060666 (10), this sequence (11), A060676 (12).
Sequence in context: A258919 A064253 A069266 * A254848 A235181 A268773
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Apr 18 2001
STATUS
approved