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 A098438 Numbers k such that (30^k - 1)/29 is prime. 10
 2, 5, 11, 163, 569, 1789, 8447, 72871, 78857, 82883 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS No other terms < 10^5. - Robert Price LINKS H. Dubner, Generalized repunit primes, Math. Comp., 61 (1993), 927-930. H. Lifchitz, Mersenne and Fermat primes field Index to primes in various ranges, form ((k+1)^n-1)/k MATHEMATICA Do[If[PrimeQ[(30^n - 1)/29], Print[n]], {n, 1, 10000}] (* Ryan Propper, Jun 25 2005 *) Select[Prime[Range[100]], PrimeQ[(30^#-1)/29]&] (* Alexander Adamchuk, Feb 11 2007 *) PROG (MAGMA) for i in [1..500] do if i mod 50 eq 0 then print "counter equals", counter; end if; if IsPrime(i) then n := 0; for j in [0..i-1] do n +:= 30^j; end for; if IsPrime(n) then print n; print i; end if; end if; end for; (PARI) is(n)=n=(30^n-1)/29; denominator(n)==1&&ispseudoprime(n) \\ Charles R Greathouse IV, Jul 01 2013 CROSSREFS Searching in the OEIS for 'repunit' gives many similar sequences. Sequence in context: A069506 A239900 A123165 * A225955 A236073 A064772 Adjacent sequences:  A098435 A098436 A098437 * A098439 A098440 A098441 KEYWORD nonn,more AUTHOR Tim Honeywill, Jon Ingram, and Paul Boddington, Oct 26 2004 EXTENSIONS a(5)-a(7), corresponding to probable primes, from Ryan Propper, Jun 25 2005 a(7) = 8447 was found by Richard Fischer in 2004. - Alexander Adamchuk, Feb 11 2007 Edited by N. J. A. Sloane Jan 25 2008 at the suggestion of Herman Jamke (hermanjamke(AT)fastmail.fm) Edited by T. D. Noe, Oct 30 2008 a(8)-a(10) from Robert Price, Dec 10 2011 STATUS approved

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Last modified March 28 07:59 EDT 2020. Contains 333079 sequences. (Running on oeis4.)