A110065 Numbers k such that 10^k - k is prime.

3, 23, 171, 903, 9911, 48107, 48449, 60959

Offset: 1

Author

Farideh Firoozbakht, Jul 11 2005

Keywords

• more
• nonn

Comments

For each n, a(n) == 3 (mod 6) or a(n) == 5 (mod 6).

There is no further term up to 16000. - Farideh Firoozbakht, Dec 02 2006

a(9) > 10^5. - Robert Price, Feb 19 2015

Crossrefs

Cf. A024115 (10^n-n).

Cf. A110066, A089379, A110067, A110068, A174175, A174176, A174177, A174178, A193881, A193882.

Programs

PARI

is(n)=isprime(10^n-n) \\ Charles R Greathouse IV, Feb 17 2017

Python

from sympy import isprime
def afind(limit):
  m, pow10 = 0, 1
  while m <= limit:
    if isprime(pow10 - m): print(m, end=", ")
    m, pow10 =  m + 1, pow10 * 10
afind(1000) # Michael S. Branicky, Mar 23 2021

Extensions

a(5) from Farideh Firoozbakht, Dec 02 2006

Definition corrected by Farideh Firoozbakht, Dec 12 2006

a(6)-a(8) from Robert Price, Feb 19 2015