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A299381
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Numbers k such that k * 18^k - 1 is prime.
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9
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1, 2, 6, 8, 10, 28, 30, 39, 45, 112, 348, 380, 458, 585, 17559, 38751, 43346, 46984, 92711
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OFFSET
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1,2
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COMMENTS
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a(20) > 400000.
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LINKS
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Table of n, a(n) for n=1..19.
Steven Harvey, Generalized Woodall Search
Wikipedia, Woodall number
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MATHEMATICA
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Select[Range[1, 10000], PrimeQ[n*18^n-1] &]
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PROG
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(PARI) for(n=1, 10000, if(isprime(n*18^n-1)), print1(n, ", ")))
(MAGMA) [n: n in [1..10000] |IsPrime(n*18^n-1)]
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CROSSREFS
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Numbers n such that n * b^n - 1 is prime: A008864 (b=1), A002234 (b=2), A006553 (b=3), A086661 (b=4), A059676 (b=5), A059675 (b=6), A242200 (b=7), A242201 (b=8), A242202 (b=9), A059671 (b=10), A299374 (b=11), A299375 (b=12), A299376 (b=13), A299377 (b=14), A299378 (b=15), A299379 (b=16), A299380 (b=17), this sequence (b=18), A299382 (b=19), A299383 (b=20).
Sequence in context: A118257 A066762 A066198 * A247984 A108417 A185078
Adjacent sequences: A299378 A299379 A299380 * A299382 A299383 A299384
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KEYWORD
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nonn,more,hard
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AUTHOR
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Tim Johannes Ohrtmann, Feb 08 2018
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STATUS
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approved
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