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A194638 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. 13
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Bisection of A194603.

Primes arising from A194636 (or 0 if no such prime exists).

LINKS

Arkadiusz Wesolowski, Table of n, a(n) for n = 1..1000

EXAMPLE

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.

MATHEMATICA

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 *)

CROSSREFS

Cf. A194591, A194600, A194603, A194606, A194607, A194608, A194635, A194636, A194637, A194639.

Cf. A038699, A050921, A076335, A180247.

Sequence in context: A126806 A279197 A121871 * A327870 A235606 A175202

Adjacent sequences:  A194635 A194636 A194637 * A194639 A194640 A194641

KEYWORD

nonn

AUTHOR

Arkadiusz Wesolowski, Aug 31 2011

STATUS

approved

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Last modified May 18 23:08 EDT 2021. Contains 344008 sequences. (Running on oeis4.)