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A194638
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Smallest prime either of the form (2*n-1)*2^k - 1 or (2*n-1)*2^k + 1, k >= 0, or 0 if no such prime exists.
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13
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2, 2, 11, 13, 17, 23, 53, 29, 67, 37, 41, 47, 101, 53, 59, 61, 67, 71, 73, 79, 83, 173, 89, 751, 97, 101, 107, 109, 113, 1889, 487, 127, 131, 269, 137, 283, 293, 149, 307, 157, 163, 167, 1361, 173, 179, 181, 373, 191, 193, 197, 809, 823, 211, 857, 6977, 223, 227
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OFFSET
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1,1
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COMMENTS
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Bisection of A194603.
Primes arising from A194636 (or 0 if no such prime exists).
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LINKS
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Arkadiusz Wesolowski, Table of n, a(n) for n = 1..1000
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EXAMPLE
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For n=4, 7*2^0-1 and 7*2^0+1 are composite, but 7*2^1-1=13 is prime, so a(4)=13.
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MATHEMATICA
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Table[n = 2*n - 1; k = 0; While[! PrimeQ[a = n*2^k - 1] && ! PrimeQ[a = n*2^k + 1], k++]; a, {n, 100}] (* Arkadiusz Wesolowski, Sep 04 2011 *)
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CROSSREFS
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Cf. A194591, A194600, A194603, A194606, A194607, A194608, A194635, A194636, A194637, A194639.
Cf. A038699, A050921, A076335, A180247.
Sequence in context: A090525 A126806 A121871 * A175202 A187430 A151365
Adjacent sequences: A194635 A194636 A194637 * A194639 A194640 A194641
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KEYWORD
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nonn
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AUTHOR
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Arkadiusz Wesolowski, Aug 31 2011
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STATUS
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approved
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