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 A056804 Numbers n such that 7*10^n + 1 is prime. 6
 1, 2, 3, 4, 5, 8, 9, 45, 136, 142, 158, 243, 923, 1235, 2196, 4650, 6119, 7324, 9543, 13494, 20310, 20360, 232920, 830865, 902708 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS 7*10^902708+1 was the 84th-largest prime in the world as of Jun 28 2013. Also largest known "base-10" form for a prime number. There are no other values of n in this sequence between 232920 and 902708 that yield a prime. - Edward A. Trice, Jul 03 2013 Apparently Edward A. Trice found another term in the gap mentioned above in May 2014. - Ray Chandler, Apr 29 2015 LINKS Makoto Kamada, Prime numbers of the form 700...001. Sabin Tabirca and Kieran Reynolds, Lacunary Prime Numbers. FORMULA a(n) = A101128(n) + 1. MATHEMATICA Do[ If[ PrimeQ[ 7*10^n + 1], Print[ n ]], {n, 0, 10000}] PROG (PARI) is(n)=ispseudoprime(7*10^n+1) \\ Charles R Greathouse IV, Feb 20 2017 CROSSREFS Cf. A101128. Sequence in context: A057911 A085266 A280431 * A305399 A101547 A047597 Adjacent sequences:  A056801 A056802 A056803 * A056805 A056806 A056807 KEYWORD more,nonn AUTHOR Robert G. Wilson v, Aug 22 2000 EXTENSIONS a(15)-a(20) from Robert G. Wilson v, Jan 19 2005 a(21)-a(22) from Kamada data by Robert Price, Dec 14 2010 a(23) from Edward A. Trice, Jan 11 2013 a(25) (thought to be a(24) at the time) from Edward A. Trice, Jun 28 2013 a(24) from Edward A. Trice, inserted by Robert G. Wilson v, May 15 2014 STATUS approved

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Last modified August 3 02:48 EDT 2021. Contains 346435 sequences. (Running on oeis4.)