A055558 Primes of the form 1999...999.

19, 199, 1999, 199999, 19999999, 199999999999999999999999999, 1999999999999999999999999999, 199999999999999999999999999999999999999999999999999999

Offset

1,1

Links

Table of n, a(n) for n=1..8.

Formula

Primes of the form 2*10^n - 1.

Example

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.

Prog

(PARI) for(n=1, 99, if(ispseudoprime(t=2*10^n-1), print1(t", "))) \\ Charles R Greathouse IV, Dec 10 2013

Crossrefs

Subsequence of A090149.

Cf. A002957, A051200.

Sequence in context: A067272 A065582 A241021 * A160452 A113596 A155670

Adjacent sequences: A055555 A055556 A055557 * A055559 A055560 A055561

Keyword

base,nonn

Author

Labos Elemer, Jul 10 2000

Status

approved