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A007371
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Numbers n such that sigma (x) = n has exactly 2 solutions.
(Formerly M4827)
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12
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12, 18, 31, 32, 54, 56, 80, 98, 104, 108, 114, 124, 126, 128, 132, 140, 152, 156, 182, 186, 210, 264, 272, 280, 308, 320, 342, 378, 390, 392, 399, 403, 408, 416, 440, 444, 448, 492, 522, 532, 570, 572, 594, 608, 630, 632, 726
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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REFERENCES
| M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards Applied Math. Series 55, 1964 (and various reprintings), p. 840.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
| M. Abramowitz and I. A. Stegun, eds., Handbook of Mathematical Functions, National Bureau of Standards, Applied Math. Series 55, Tenth Printing, 1972 [alternative scanned copy].
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MATHEMATICA
| a = Table[ 0, {750} ]; Do[ s = DivisorSigma[ 1, n ]; If[ s < 751, a[ [ s ] ]++ ], {n, 1, 750} ]; Select[ Range[ 750 ], a[ [ # ] ] == 2 & ]
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CROSSREFS
| Cf. A007369, A007370, A007372, etc.
Sequence in context: A138636 A075281 A171179 * A079479 A162694 A197464
Adjacent sequences: A007368 A007369 A007370 * A007372 A007373 A007374
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KEYWORD
| nonn
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AUTHOR
| N. J. A. Sloane (njas(AT)research.att.com), Mira Bernstein, Robert G. Wilson v (rgwv(AT)rgwv.com)
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