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Primes of the form 10^i + 10^j - 1.
1

%I #13 May 15 2021 15:29:01

%S 19,109,199,1009,1999,10009,10099,100999,199999,1000099,1000999,

%T 19999999,1000000009,1000009999,1000099999,1009999999,10000000999,

%U 10000099999,10999999999,100999999999,1000000009999,1000000999999,1099999999999,10000000000099,10009999999999,100000000000099,100000009999999

%N Primes of the form 10^i + 10^j - 1.

%C Primes p such that p+1 is in A052216.

%C Primes of the following form in base 10: 1, followed by 0 or more 0's, then 1 or more 9's.

%H Robert Israel, <a href="/A306855/b306855.txt">Table of n, a(n) for n = 1..2000</a>

%p select(isprime, [seq(seq(10^n+10^m-1, m=1..n),n=1..15)]);

%t Select[Flatten[Table[FromDigits[Join[PadRight[{1},n,0],PadRight[{},m,9]]],{n,20},{m,20}]],PrimeQ]//Sort (* _Harvey P. Dale_, May 15 2021 *)

%Y Cf. A052216. Subsequence of A199329.

%K nonn,base

%O 1,1

%A _Robert Israel_, Mar 13 2019