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 A062576 Numbers n such that 10^n - 9^n is prime. 5
 2, 3, 7, 11, 19, 29, 401, 709, 2531, 15787, 66949, 282493 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Terms > 1000 are often only strong pseudoprimes. All terms are prime. - Alexander Adamchuk, Apr 27 2008 LINKS Henri & Renaud Lifchitz, PRP Records. EXAMPLE 10^2 - 9^2 = 100 - 81 = 19, which is prime, hence 2 is in the sequence. 10^3 - 9^3 = 1000 - 729 = 271, which is prime, hence 3 is in the sequence. 10^4 - 9^4 = 10000 - 6561 = 3439 = 19 * 181, which is not prime, hence 4 is not in the sequence. MATHEMATICA Select[Range[1000], PrimeQ[10^# - 9^#] &] (* Alonso del Arte, Sep 06 2013 *) PROG (PARI) is(n)=ispseudoprime(10^n-9^n) \\ Charles R Greathouse IV, Feb 20 2017 CROSSREFS Cf. A000043, A057468, A059801, A059802, A059803 (9^n-8^n is prime), A062572-A062666. Cf. A016189 = 10^n - 9^n, and A199819 (primes of this form). Sequence in context: A235633 A232232 A232233 * A238686 A079739 A210394 Adjacent sequences:  A062573 A062574 A062575 * A062577 A062578 A062579 KEYWORD nonn,hard AUTHOR Mike Oakes, May 18 2001, May 19 2001 EXTENSIONS Three more terms 15787, 66949 and 282493 found by Jean-Louis Charton in 2004 and 2007 STATUS approved

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Last modified May 26 13:49 EDT 2020. Contains 334626 sequences. (Running on oeis4.)