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A128002
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Numbers n such that (31^n - 1)/30 is prime.
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9
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OFFSET
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1,1
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COMMENTS
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9973 is a term found by Richard Fischer in 2004. - Alexander Adamchuk, Feb 11 2007
No other terms < 101833. - Robert Price, Nov 26 2011
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LINKS
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Table of n, a(n) for n=1..7.
H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
H. Lifchitz, Mersenne and Fermat primes field
Index to primes in various ranges, form ((k+1)^n-1)/k
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MATHEMATICA
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Select[Prime[Range[100]], PrimeQ[(31^#-1)/30]&]
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PROG
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(PARI) is(n)=ispseudoprime((31^n-1)/30) \\ Charles R Greathouse IV, Feb 17 2017
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CROSSREFS
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Sequence in context: A319304 A144861 A066436 * A301695 A301725 A278920
Adjacent sequences: A127999 A128000 A128001 * A128003 A128004 A128005
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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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More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 05 2008
a(6) = 101111 by Robert Price, Nov 26 2011
a(7) = 535571 from Alexander Zhirkov, added by Paul Bourdelais, Jan 28 2021
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STATUS
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approved
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