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A216529 Numbers n such that (10^n-1)/9 is prime and can be written in the form a^2 + 3*b^2. 0

%I

%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

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Last modified May 15 06:18 EDT 2021. Contains 343909 sequences. (Running on oeis4.)