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
KEYWORD
nonn
AUTHOR
Arkadiusz Wesolowski, Aug 30 2011
STATUS
approved