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 A056805 Numbers n such that 6*10^n+1 is prime. 10
 0, 1, 2, 8, 9, 15, 20, 26, 38, 45, 65, 112, 244, 303, 393, 560, 839, 1009, 1019, 1173, 1334, 2236, 2629, 4426, 8848, 20812, 37744, 72926, 86287 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS From the Kamada data, Edward Trice reports that 231617 and 522127 are in this sequence. But these may not be the next ones.  There are no others less than 2*10^5, however. - Robert Price, Jul 09 2015 LINKS Makoto Kamada, Prime numbers of the form 600...001. Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers. FORMULA a(n) = A101517(n-1) + 1. EXAMPLE n=2 => (6*10^2+1)=601, which is prime. MATHEMATICA Do[ If[ PrimeQ[ 6*10^n + 1], Print[ n ]], {n, 0, 10000}] PROG (PARI) is(n)=isprime(6*10^n+1) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A056716, A101517. Sequence in context: A032928 A287564 A158458 * A226825 A046679 A004999 Adjacent sequences:  A056802 A056803 A056804 * A056806 A056807 A056808 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Aug 22 2000 EXTENSIONS a(22)-a(25) from Hugo Pfoertner, Feb 11 2004 a(26)=20812 from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Dec 27 2007 a(27)=37744 from Jason Earls, Mar 07 2008 a(28)-a(29) from Kamada data by Robert Price, Dec 09 2010 STATUS approved

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Last modified December 5 17:42 EST 2019. Contains 329768 sequences. (Running on oeis4.)