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A060666
Numbers k such that sigma(x) = k has exactly 10 solutions.
12
504, 864, 960, 1152, 1260, 2400, 3276, 3888, 4992, 6696, 7020, 7644, 8892, 9672, 9984, 11172, 11200, 11376, 11616, 11856, 12936, 13728, 13888, 14136, 14280, 15480, 15876, 15984, 17808, 19488, 21336, 22608, 23688, 24738, 24840, 25080
OFFSET
1,1
EXAMPLE
504 = sigma(204) = sigma(220) = sigma(224) = sigma(246) = sigma(284) = sigma(286) = sigma(334) = sigma(415) = sigma(451) = sigma(504).
MATHEMATICA
a = Table[ 0, {30000} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 30001, a[ [ s ] ]++ ], {n, 1, 30000} ]; Select[ Range[ 30000 ], a[ [ # ] ] == 10 & ]
PROG
(PARI) is(k) = invsigmaNum(k) == 10 \\ 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), this sequence (10), A060678 (11), A060676 (12).
Sequence in context: A045212 A262873 A228164 * A335654 A226265 A277114
KEYWORD
nonn,changed
AUTHOR
Robert G. Wilson v, Apr 18 2001
STATUS
approved