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Search: id:A066808
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| A066808 |
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F(n)-1 mod 2^n+1 with F(n)= n-th Fermat number = 1+2^2^n. |
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+0
1
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| 1, 1, 4, 1, 4, 16, 4, 1, 256, 16, 4, 4081, 4, 16, 256, 1, 4, 261121, 4, 65536, 256, 16, 4, 65536, 33554305, 16, 67108864, 65536, 4, 16, 4, 1, 256, 16, 262144, 68451041281, 4, 16, 256, 65536, 4, 4398042316801, 4, 65536, 35184371957761, 16, 4
(list; graph; listen)
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OFFSET
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1,3
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COMMENT
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All terms except n=12,18,25,36,42,45,48,55 result in a(n) that are powers of 2, whereas these exceptions (4081, 261121, 33554305, 68451041281, 4398042316801, 35184371957761, 281474976645121, 36020000925941761) are all odd.
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LINKS
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Chris Caldwell : The Prime Glossary
Eric Weisstein
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FORMULA
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F(n)-1=1 mod (2^n+1) for all n=2^k because F(n)=2+ F(1)F(2)..F(n-1)
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MATHEMATICA
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Table[ PowerMod[ 2, 2^n, 2^n+1 ], {n, 64} ]
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CROSSREFS
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Cf. A004249, A007516, A000215, A019434.
Sequence in context: A007891 A055886 A132478 this_sequence A033918 A136467 A079188
Adjacent sequences: A066805 A066806 A066807 this_sequence A066809 A066810 A066811
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KEYWORD
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nonn
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AUTHOR
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Wouter Meeussen (wouter.meeussen(AT)pandora.be), Jan 19 2002
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