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A127995
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Numbers n such that (20^n - 1)/19 is prime.
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17
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OFFSET
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1,1
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REFERENCES
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H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
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LINKS
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Table of n, a(n) for n=1..7.
H. Lifchitz, Mersenne and Fermat primes field
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MATHEMATICA
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Select[Prime[Range[100]], PrimeQ[(20^#-1)/19]&]
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PROG
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(Other) PFGW v3.3.1 [From Paul Bourdelais, Mar 05 2010]
(Other) PFGW v3.3.1 [From Paul Bourdelais, Mar 08 2010]
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CROSSREFS
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Cf. A028491, A004061, A004062, A004063, A004023, A005808, A004064, A016054, A006032, A006033, A006034, A006035, A127996, A127997, A127998, A127999, A128000, A098438, A128002, A128003, A128004, A128005.
Sequence in context: A128346 A128031 A194128 * A119141 A117769 A030377
Adjacent sequences: A127992 A127993 A127994 * A127996 A127997 A127998
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KEYWORD
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hard,more,nonn
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AUTHOR
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Alexander Adamchuk, Feb 11 2007
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EXTENSIONS
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One more term from Ryan Propper (rpropper(AT)stanford.edu), Mar 29 2007
a(5)=31013 & a(6)=48859 are probable primes discovered by Paul Bourdelais, Mar 05 2010
a(7)=61403 is a probable prime discovered by Paul Bourdelais, Mar 08 2010
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STATUS
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approved
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