This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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: A090525 A126806 A121871 * A175202 A187430 A151365 Adjacent sequences:  A194635 A194636 A194637 * A194639 A194640 A194641 KEYWORD nonn AUTHOR Arkadiusz Wesolowski, Aug 31 2011 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Puzzles | Hot | Classics
Recent Additions | More pages | Superseeker | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .