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A194608 Smallest prime either of the form prime(n)*2^k - 1 or prime(n)*2^k + 1, k >= 0, or 0 if no such prime exists, where prime(n) denotes the n-th prime number. 13
3, 2, 11, 13, 23, 53, 67, 37, 47, 59, 61, 73, 83, 173, 751, 107, 1889, 487, 269, 283, 293, 157, 167, 179, 193, 809, 823, 857, 6977, 227, 509, 263, 547, 277, 1193, 2417, 313, 653, 2671, 347, 359, 1447, 383, 773, 787, 397, 421, 1783, 907, 457, 467, 479, 493567 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
Primes arising from A194606 (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[p = Prime[n]; k = 0; While[! PrimeQ[a = p*2^k - 1] && ! PrimeQ[a = p*2^k + 1], k++]; a, {n, 100}] (* Arkadiusz Wesolowski, Sep 04 2011 *)
CROSSREFS
Sequence in context: A074246 A134426 A122672 * A297870 A052973 A087956
KEYWORD
nonn
AUTHOR
STATUS
approved

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Last modified April 23 07:16 EDT 2024. Contains 371905 sequences. (Running on oeis4.)