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Primes of the form k followed by a 0 and k 9's.
1

%I #8 Mar 24 2020 08:43:39

%S 109,2099,409999,1909999999999999999999,

%T 2809999999999999999999999999999,

%U 41099999999999999999999999999999999999999999,7609999999999999999999999999999999999999999999999999999999999999999999999999999

%N Primes of the form k followed by a 0 and k 9's.

%C Primes of the form k*10^(k+1) + 10^k - 1.

%o (PARI) lista(nn) = for(k=1, nn, if(ispseudoprime(q=k*10^(k+1)+10^k-1), print1(q, ", "))); \\ _Jinyuan Wang_, Mar 24 2020

%Y Cf. A141311, A145851.

%K nonn

%O 1,1

%A _Lekraj Beedassy_, Oct 21 2008