OFFSET
1,1
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
KEYWORD
base,nonn
AUTHOR
Labos Elemer, Jul 10 2000
STATUS
approved