A111391 Numbers k such that 11*10^k - 1 is prime.

1, 9, 11, 17, 22, 29, 36, 37, 52, 166, 448, 2011, 3489, 4871, 6982, 10024, 16974, 33287, 47364, 58873, 126160, 234424, 382881, 524706

Offset: 1

Author

Robert G. Wilson v, Nov 15 2005

Keywords

• more
• nonn

Comments

Numbers k such that 10^(k+1) + (10^k-1) is a prime.

Links

• Gary Barnes, Primes of the form k*10^n-1
• Makoto Kamada, Search for 109w.

Crossrefs

Cf. A096209.

Programs

Mathematica

Do[ If[ PrimeQ[10^(n + 1) + (10^n - 1)], Print[n]], {n, 9500}]

PARI

is(n)=ispseudoprime(11*10^n-1) \\ Charles R Greathouse IV, Jun 12 2017

Extensions

a(16)-a(19) from Ray Chandler, Sep 16 2013

a(20)-a(21) from P. Kurtovic submitted by Ray Chandler, Sep 17 2013

a(22)-a(24) from Kamada data by Tyler Busby, Apr 14 2024