%I

%S 2,127,877

%N Numbers n such that 22^n - 21^n is prime.

%C All terms are prime.

%C No other terms less than 10^5. - _Robert Price_, May 28 2012

%o (PARI) is(n)=ispseudoprime(22^n-21^n) \\ _Charles R Greathouse IV_, Jun 12 2017

%Y Cf. A000043, A057468, A059801, A059802, A062572-A062666.

%K nonn,hard,bref,more

%O 1,1

%A _Mike Oakes_, May 18 2001, May 19 2001