

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

Table of n, a(n) for n=1..12.
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^n9^n) \\ Charles R Greathouse IV, Feb 20 2017


CROSSREFS

Cf. A000043, A057468, A059801, A059802, A059803 (9^n8^n is prime), A062572A062666.
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 JeanLouis Charton in 2004 and 2007


STATUS

approved



