login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 19 03:18 EDT 2024. Contains 370952 sequences. (Running on oeis4.)