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A127996
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Numbers n such that (21^n - 1)/20 is prime.
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13
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OFFSET
| 1,1
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REFERENCES
| H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930.
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LINKS
| H. Lifchitz, Mersenne and Fermat primes field
Paul Bourdelais,A Generalized Repunit Conjecture [From Paul Bourdelais (pbourdelais(AT)radiantblue.com), Apr 26 2010]
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MATHEMATICA
| Select[Prime[Range[100]], PrimeQ[(21^#-1)/20]&]
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PROG
| (Other) PFGW v3.3.1 [From Paul Bourdelais (pbourdelais(AT)radiantblue.com), Apr 26 2010]
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CROSSREFS
| Cf. A028491, A004061, A004062, A004063, A004023, A005808, A004064, A016054, A006032, A006033, A006034, A006035. Cf. A127995, A127997, A127998, A127999, A128000, A098438, A128002, A128003, A128004, A128005.
Sequence in context: A203162 A176804 A078116 * A032008 A061368 A145701
Adjacent sequences: A127993 A127994 A127995 * A127997 A127998 A127999
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KEYWORD
| hard,more,nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Feb 11 2007
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EXTENSIONS
| a(6)=156217 is a probable prime discovered by Paul Bourdelais (pbourdelais(AT)radiantblue.com), Apr 26 2010
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