A306855 Primes of the form 10^i + 10^j - 1.

19, 109, 199, 1009, 1999, 10009, 10099, 100999, 199999, 1000099, 1000999, 19999999, 1000000009, 1000009999, 1000099999, 1009999999, 10000000999, 10000099999, 10999999999, 100999999999, 1000000009999, 1000000999999, 1099999999999, 10000000000099, 10009999999999, 100000000000099, 100000009999999

Offset: 1

Author

Robert Israel, Mar 13 2019

Keywords

• nonn
• base

Comments

Primes p such that p+1 is in A052216.

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

Links

• Robert Israel, Table of n, a(n) for n = 1..2000

Crossrefs

Cf. A052216. Subsequence of A199329.

Programs

Maple

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

Mathematica

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