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A065854
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Smallest prime q such that (p^q-1)/(p-1) is a prime, where p = prime(n).
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5
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2, 3, 3, 5, 17, 5, 3, 19, 5, 5, 7, 13, 3, 5, 127, 11, 3, 7, 19, 3, 5, 5, 5, 3, 17, 3, 19, 17, 17, 23, 5, 3, 11, 163, 7, 13, 17, 7, 3, 3, 19, 17, 17, 5, 31, 577, 41, 239, 5, 11, 113, 5, 17, 7, 23, 5
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| a(n) = 2*A065813(n)+1, n > 1.
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LINKS
| Andy Steward, Titanic Prime Generalized Repunits
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MATHEMATICA
| Do[p = Prime[n]; k = 1; While[ !PrimeQ[ (p^Prime[k] - 1)/(p - 1)], k++ ]; Print[ Prime[k]], {n, 1, 56} ]
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PROG
| (PARI) { allocatemem(932245000); for (n=1, 100, p=prime(n); q=2; while (!isprime((p^q - 1)/(p - 1)), q=nextprime(q + 1)); write("b065854.txt", n, " ", q) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Nov 01 2009]
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CROSSREFS
| Cf. A084740 (least k such that (n^k-1)/(n-1) is prime).
Sequence in context: A045626 A154923 A154693 * A064776 A096659 A154695
Adjacent sequences: A065851 A065852 A065853 * A065855 A065856 A065857
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KEYWORD
| hard,nonn
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AUTHOR
| Vladeta Jovovic (vladeta(AT)eunet.rs), Nov 26 2001
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