This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A057173 Numbers n such that (7^n + 1)/8 is a prime. 13
 3, 17, 23, 29, 47, 61, 1619, 18251, 106187, 201653 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS (7^1619+1)/8, a 1368-digit number, has been certified prime with Primo. - Rick L. Shepherd, May 19 2002 LINKS J. Brillhart et al., Factorizations of b^n +- 1, Contemporary Mathematics, Vol. 22, Amer. Math. Soc., Providence, RI, 3rd edition, 2002. H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7. H. Lifchitz, Mersenne and Fermat primes field Eric Weisstein's World of Mathematics, Repunit MATHEMATICA lst={}; Do[p=(7^n+1)/8; If[PrimeQ[p], AppendTo[lst, n]], {n, 7!}]; lst (* Vladimir Joseph Stephan Orlovsky, Sep 29 2008 *) PROG (PARI) isok(n) = (denominator(p=(7^n+1)/8)==1) && isprime(p); \\ Michel Marcus, Oct 30 2017 CROSSREFS Sequence in context: A019380 A296937 A126692 * A109371 A272176 A082372 Adjacent sequences:  A057170 A057171 A057172 * A057174 A057175 A057176 KEYWORD nonn,more AUTHOR N. J. A. Sloane, Sep 15 2000 EXTENSIONS a(9)=106187 is a probable prime based on Fermat primality testing and trial factoring to 2E13. - Paul Bourdelais, Apr 07 2008 a(10)=201653 is a probable prime discovered by Paul Bourdelais, Feb 17 2010 STATUS approved

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

Last modified March 23 17:10 EDT 2018. Contains 301123 sequences. (Running on oeis4.)