|
%I #16 Jun 13 2017 13:51:43
%S 19,49081,109297,270343
%N Numbers n such that (10^n-1)/9 is prime and can be written in the form a^2 + 3*b^2.
%C The exponent is congruent to 1 mod 3.
%H Samuel S. Wagstaff, Jr. <a href="http://homes.cerias.purdue.edu/~ssw/cun/index.html">The Cunningham Project</a>
%o (PARI) is(n)=my(t=10^n\9); ispseudoprime(t) && #bnfisintnorm(bnfinit(z^2+z+1), t) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y Cf. A004023, A003136.
%K nonn
%O 1,1
%A _V. Raman_, Sep 08 2012
| 