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Search: id:A078426
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| A078426 |
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Numbers n such that there is no solution to the equation sigma(x)=2^n, where sigma(x) denotes the sum of the divisors of x. |
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+0
5
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| 1, 4, 6, 11, 470, 475, 477, 480, 482, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 496, 497, 498, 499, 500, 501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512, 513, 514, 515, 516, 517, 518, 519, 520, 522, 525, 527, 532, 1077, 1082
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Numbers that are not a sum of distinct Mersenne primes (A000043). - Vladeta Jovovic (vladeta(AT)eunet.rs), Jan 01 2003
Comment from T. D. Noe, Oct 12 2006: Because there is a large gap between the 31st and 32nd Mersenne primes, all n between 704338 and 756839 are in this sequence.
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REFERENCES
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S. Kravitz, "Beware of the Fifth", Solution to Problem 2309, Journal of Recreational Mathematics, 29(1):76 Baywood NY 1998.
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LINKS
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T. D. Noe, Table of n, a(n) for n=1..350
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EXAMPLE
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a(2)=4 because no positive integer value of x can satisfy sigma(x)=2^4=16.
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CROSSREFS
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Cf. A063883, A046528.
Sequence in context: A066155 A105308 A116983 this_sequence A114413 A152678 A110758
Adjacent sequences: A078423 A078424 A078425 this_sequence A078427 A078428 A078429
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KEYWORD
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nonn
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AUTHOR
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Shyam Sunder Gupta (guptass(AT)rediffmail.com), Dec 29 2002
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EXTENSIONS
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More terms from Vladeta Jovovic (vladeta(AT)eunet.rs), Jan 01 2003
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