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A013597
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a(n) = nextprime(2^n) - 2^n.
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23
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1, 1, 1, 3, 1, 5, 3, 3, 1, 9, 7, 5, 3, 17, 27, 3, 1, 29, 3, 21, 7, 17, 15, 9, 43, 35, 15, 29, 3, 11, 3, 11, 15, 17, 25, 53, 31, 9, 7, 23, 15, 27, 15, 29, 7, 59, 15, 5, 21, 69, 55, 21, 21, 5, 159, 3, 81, 9, 69, 131, 33, 15, 135, 29, 13, 131, 9, 3, 33, 29, 25, 11, 15, 29
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OFFSET
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0,4
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COMMENTS
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If (for n>0) a(n)=1, then n is a power of 2 and 2^n+1 is a Fermat prime. n=1,2,4,8,16 are probably the only indices with this property. - Franz Vrabec, Sep 27 2005
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LINKS
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FORMULA
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MAPLE
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nextprime(2^n)-2^n ;
end proc:
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MATHEMATICA
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PROG
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(PARI) a(n) = nextprime(2^n+1) - 2^n; \\ Michel Marcus, Nov 06 2015
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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James Kilfiger (mapdn(AT)csv.warwick.ac.uk)
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STATUS
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approved
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