OFFSET
1,1
COMMENTS
Terms greater than 1000 may correspond to (unproven) strong pseudoprimes.
PROG
(PARI) is(n)=ispseudoprime(21^n-20^n) \\ Charles R Greathouse IV, Jun 13 2017
CROSSREFS
KEYWORD
nonn,hard
AUTHOR
Mike Oakes, May 18 2001, May 19 2001
EXTENSIONS
a(8) from Jean-Louis Charton, Feb 29 2012
a(9) and a(10) from Robert Price, May 30 2012
Edited by M. F. Hasler, Sep 16 2013
a(11) added by Jean-Louis Charton, Nov 24 2014
a(12) added by Jean-Louis Charton, Feb 05 2015
a(13) added by Jean-Louis Charton, Feb 18 2015
STATUS
approved