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Search: id:A095380
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| A095380 |
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Number of integers not exceeding 2^n that are impossible as sum-of-divisors of other numbers. |
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+0
1
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| 1, 1, 2, 6, 15, 34, 75, 162, 337, 706, 1466, 2995, 6119, 12450, 25248, 51158, 103450, 209010
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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Conjecture: ratio of non-sigma numbers tends to one. Increasing majority of numbers is impossible as a sum of divisors.
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FORMULA
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a[n] is the number of terms in A007369 not exceeding 2^n
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EXAMPLE
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n=5: {2,5,9,10,11,16,17,19,21,22,23,25,26,27,29} is the
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MATHEMATICA
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Table[{a={}; Do[s=DivisorSigma[1, n]; a=Append[a, s], {n, 1, 2^j}];
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CROSSREFS
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Cf. A093532, A007369.
Adjacent sequences: A095377 A095378 A095379 this_sequence A095381 A095382 A095383
Sequence in context: A056520 A078406 A101352 this_sequence A073838 A014303 A076060
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KEYWORD
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nonn
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AUTHOR
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Labos E. and Antti Karttunen (labos(AT)ana.sote.hu; his-firstname.his-surname(AT)iki.fi), Jun 07 2004
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