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Search: id:A114705
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| A114705 |
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Sum of divisors of 2^n + 3^n. |
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+0
2
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| 6, 14, 48, 98, 372, 868, 2784, 7236, 27744, 64708, 215040, 541156, 1947840, 5168548, 23046144, 43129476, 155189760, 444228512, 1398675600, 3623742864, 14636428992, 33799504228, 113272236000, 299806597512, 1154553386688
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The terms are never squares. For n>=2, 2^n+3^n falls into a pattern of quadratic non-residues, taken modulo 20: 13, 15, 17, 15, 13, 15, 17, 15, ... - Jack Brennen, Dec 25 2005
a(n) is always even because 2^n+3^n is never a quadratic residue modulo 15. - Jose Brox (tautocrona(AT)terra.es), Dec 27 2005
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EXAMPLE
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a(3)=48 because 2^3+3^3=8+27=35 has divisors 1,5,7,35 sum of which is 48.
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MATHEMATICA
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Table[DivisorSigma[1, 2^n+3^n], {n, 1, 30}]
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CROSSREFS
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Cf. A000203.
Sequence in context: A093369 A130443 A005515 this_sequence A107301 A118432 A032404
Adjacent sequences: A114702 A114703 A114704 this_sequence A114706 A114707 A114708
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KEYWORD
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nonn
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AUTHOR
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Zak Seidov (zakseidov(AT)yahoo.com), Dec 26 2005
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