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A215698
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Number of primes of the form 1 + b^256 for 1 < b < 10^n.
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8
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OFFSET
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1,3
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COMMENTS
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Primes 1 + b^256 are a form of generalized Fermat primes.
It is conjectured that a(n) is asymptotic to 0.0290422*li(10^n)
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LINKS
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EXAMPLE
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a(3) = 4 because the generalized Fermat numbers F_8(b) where b<10^3 are prime only for b: 278, 614, 892, 898.
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PROG
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(PARI) a(n) = sum(b=1, 10^n/2-1, isprime((2*b)^256+1))
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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