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A050226
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Sum of divisor function d(n) (A000005) up to n is divisible by n.
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15
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1, 4, 5, 15, 42, 44, 47, 121, 336, 340, 347, 930, 2548, 6937, 6947, 51322, 379097, 379131, 379133, 2801205, 20698345, 56264090, 56264197, 152941920, 152942012, 8350344420, 61701166395, 455913379395, 455913379831, 1239301050694
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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REFERENCES
| Julian Havil, "Gamma: Exploring Euler's Constant", Princeton University Press, Princeton and Oxford, pp. 112-113, 2003.
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FORMULA
| Sum {1..n} d(n) = n*k, k is an integer, d(n) = number of divisors of n..
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EXAMPLE
| For n = 15 the sum is 1 + 2 + 2 + 3 + 2 + 4 + 2 + 4 + 3 + 4 + 2 + 6 + 2 + 4 + 4 = 45 which is divisible by 15.
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MATHEMATICA
| s = 0; Do[ s = s + DivisorSigma[ 0, n ]; If[ Mod[ s, n ] == 0, Print[ n ] ], {n, 1, 2*10^9} ]
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CROSSREFS
| Cf. A000005, A006218, A057494, A085567, A085829.
Sequence in context: A184244 A006491 A051721 * A119562 A166590 A085768
Adjacent sequences: A050223 A050224 A050225 * A050227 A050228 A050229
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KEYWORD
| nonn,nice
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AUTHOR
| Labos E. (labos(AT)ana.sote.hu), Dec 20 1999
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Sep 21 2000. Further terms from Naohiro Nomoto (6284968128(AT)geocities.co.jp), Aug 03 2001.
a(26)-a(30) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Dec 21 2008
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