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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
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1, 1, 2, 6, 15, 34, 75, 162, 337, 706, 1466, 2995, 6119, 12450, 25248, 51158, 103450, 209010, 421681, 850322, 1712673, 3447970, 6937759, 13952296, 28049834, 56369395, 113241087, 227428919, 456641954, 916642515, 1839651364, 3691364919, 7405635242
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| 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
| a(n) is the number of terms in A007369 not exceeding 2^n
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EXAMPLE
| n=5: {2,5,9,10,11,16,17,19,21,22,23,25,26,27,29} are the 15 terms <= 2^5 in A007369.
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MATHEMATICA
| Table[{a={}; Do[s=DivisorSigma[1, n]; a=Append[a, s], {n, 1, 2^j}];
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CROSSREFS
| Cf. A007369.
Sequence in context: A078406 A101352 A192980 * A073838 A014303 A076060
Adjacent sequences: A095377 A095378 A095379 * A095381 A095382 A095383
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KEYWORD
| nonn
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AUTHOR
| Labos E. and Antti Karttunen (labos(AT)ana.sote.hu; his-firstname.his-surname(AT)iki.fi), Jun 07 2004
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EXTENSIONS
| a(19)-a(31) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Nov 30 2008
a(32)-a(33) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Aug 06 2011
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