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 A052333 Riesel problem: start with n; repeatedly double and add 1 until reach a prime. Sequence gives prime reached, or 0 if no prime is ever reached. 13
 3, 5, 7, 19, 11, 13, 31, 17, 19, 43, 23, 103, 223, 29, 31, 67, 71, 37, 79, 41, 43, 367, 47, 199, 103, 53, 223, 463, 59, 61, 127, 131, 67, 139, 71, 73, 151, 311, 79, 163, 83, 5503, 738197503, 89, 367, 751, 191, 97, 199, 101, 103, 211, 107, 109, 223, 113, 463 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Smallest prime of form (n+1)*2^k-1 for k >= 1 (or 0 if no such prime exists). a(509202)=0 (i.e. never reaches a prime) - Chris Nash (chris_nash(AT)hotmail.com). (Of course this is related to the entry 509203 of A076337.) a(73) is a 771-digit prime reached after 2552 iterations - Warut Roonguthai. This was proved to be a prime by Paul Jobling (Paul.Jobling(AT)WhiteCross.com) using PrimeForm and by Ignacio Larrosa CaĆ±estro using Titanix (http://www.znz.freesurf.fr/pages/titanix.html). [Oct 30 2000] LINKS Ray Ballinger and Wilfrid Keller, The Riesel Problem: Definition and Status EXAMPLE a(4)=19 because 4 -> 9 (composite) -> 19 (prime). MATHEMATICA Table[NestWhile[2#+1&, 2n+1, !PrimeQ[#]&], {n, 60}] (* Harvey P. Dale, May 08 2011 *) PROG (PARI) a(n)=while(!isprime(n=2*n+1), ); n \\ oo loop when a(n) = 0. - Charles R Greathouse IV, May 08, 2011 CROSSREFS Cf. A050412 (values of n), A051914, A052334, A052339, A052340, A040081. Sequence in context: A064080 A184875 A112986 * A074106 A002261 A263257 Adjacent sequences:  A052330 A052331 A052332 * A052334 A052335 A052336 KEYWORD nonn,nice AUTHOR Christian G. Bower, Dec 19 1999 STATUS approved

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Last modified October 15 00:14 EDT 2019. Contains 328025 sequences. (Running on oeis4.)