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%I #17 Jan 15 2021 02:04:05
%S 19,199,1999,199999,19999999,199999999999999999999999999,
%T 1999999999999999999999999999,
%U 199999999999999999999999999999999999999999999999999999
%N Primes of the form 1999...999.
%F Primes of the form 2*10^n - 1.
%e 2*10^n - 1 is prime for {1,2,3,5,7,26,27,53,147,236,248,386,401}; in each of these numbers, the digit '9' appears n times.
%o (PARI) for(n=1,99,if(ispseudoprime(t=2*10^n-1),print1(t", "))) \\ _Charles R Greathouse IV_, Dec 10 2013
%Y Subsequence of A090149.
%Y Cf. A002957, A051200.
%K base,nonn
%O 1,1
%A _Labos Elemer_, Jul 10 2000
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