login
This site is supported by donations to The OEIS Foundation.

 

Logo

Invitation: celebrating 50 years of OEIS, 250000 sequences, and Sloane's 75th, there will be a conference at DIMACS, Rutgers, Oct 9-10 2014.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A078686 Primes p_i such that 2^i - p_i is also prime. 5
5, 31, 67, 89, 101, 283, 503, 1039, 1129, 2069, 3457, 5641, 45763, 71483, 86599, 112921, 161411, 210173, 211007, 232741, 245269, 479029 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The original definition ("Primes p such that the minimum value of |p-2^x|, x>0, is also a prime") produces A188677, not the terms shown here. - N. J. A. Sloane, Apr 01 2011.

The mystery of this definition was solved by Robert G. Wilson v, Jul 06 2014, who also remarks that if instead we ask for odd primes, and therefore the index is one less than that for all primes, the sequence would begin: 11, 13, 17, 19, 23, 37, 61, 233, 257, 1553, 2879, 4919, 6389, 7621, 8081, 35593, 37951, 96263, 206419, ..., . If we count 1 amongst the primes (A008578), then the sequence would begin: 2, 3, 5, 11, 17, 167, 193, 197, 433, 4111, 9173, 42929, 95279, 98897, 139409, 142567, 228617, ..., .

LINKS

Table of n, a(n) for n=1..22.

EXAMPLE

a(1)=5 since 5 is the third prime number and 2^3-5 = 3 is prime. - Robert G. Wilson v, Jul 06 2014

MATHEMATICA

p = 2; lst = {}; While[p < 760001, If[ PrimeQ[ 2^PrimePi@ p - p], AppendTo[lst, p]; Print@ p]; p = NextPrime@ p]; lst (* Robert G. Wilson v, Jul 06 2014 *)

CROSSREFS

Cf. A242944, A188677.

Sequence in context: A245523 A147033 A125743 * A031908 A139862 A102732

Adjacent sequences:  A078683 A078684 A078685 * A078687 A078688 A078689

KEYWORD

nonn

AUTHOR

Benoit Cloitre, Dec 17 2002

EXTENSIONS

Edited (corrected title) and extended by Robert G. Wilson v, Jul 06 2014

STATUS

approved

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

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

Last modified August 27 23:36 EDT 2014. Contains 246151 sequences.