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A058934
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Numbers n such that 2*5^n + 1 is prime.
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1
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0, 1, 3, 13, 45, 105, 159, 297, 1443, 2977, 3699, 11709, 12357, 43165, 121995
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OFFSET
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1,3
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COMMENTS
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a(n) is odd for n>0. Next term > 17200. - Julián Aguirre, Apr 22 2011
a(16) > 2*10^5. - Robert Price, Mar 14 2015
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LINKS
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Table of n, a(n) for n=1..15.
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EXAMPLE
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a(3)=13 and 1+2*5^13=2441406251 is prime.
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MATHEMATICA
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Select[Range[0, 16000], PrimeQ[2*5^#+1]&] (* Julián Aguirre, Apr 22 2011 *)
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PROG
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(Sage)
[n for n in range(1500) if is_prime(2*5^n+1)]
# Julián Aguirre, Apr 22 2011
(PARI) is(n)=ispseudoprime(2*5^n+1) \\ Charles R Greathouse IV, Jun 12 2017
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CROSSREFS
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Cf. A003306 (2*3^n + 1 is prime), A120375 (2*5^n-1 is prime).
Sequence in context: A095863 A136520 A212416 * A141088 A187915 A115128
Adjacent sequences: A058931 A058932 A058933 * A058935 A058936 A058937
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KEYWORD
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nonn,more
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AUTHOR
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Labos Elemer, Jan 12 2001
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EXTENSIONS
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Edited by Joerg Arndt, Apr 22 2011
Terms 1443,...,12357 from Julián Aguirre, Apr 22 2011
a(14)-a(15) from Robert Price, Mar 14 2015
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STATUS
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approved
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