A278471 Numbers k such that 10^k - 2001 is prime.

16, 18, 38, 82, 98, 318, 1106, 1914, 2438, 2640, 3156, 10330, 19278, 31976, 41140

Offset: 1

Author

Vincenzo Librandi, Nov 28 2016

Keywords

• nonn
• more

Comments

For n>3, numbers such that n-4 occurrences of the digit 9 followed by the digits 7999 is prime.

Examples

			Initial terms and primes associated:
a(1) = 16, 9999999999997999;
a(2) = 18, 999999999999997999;
a(3) = 38, 99999999999999999999999999999999997999; etc.
		

Links

• Makoto Kamada, Factorization of near-repdigit-related numbers.

Crossrefs

Cf. similar sequences listed in A278470.

Programs

Magma

[n: n in [3..700] | IsPrime(10^n-2001)];

Mathematica

Select[Range[3, 10000], PrimeQ[10^# - 2001] &]

PARI

isok(n) = isprime(10^n - 2001); \\ Michel Marcus, Dec 03 2016

Extensions

a(12) from Michael S. Branicky, Jan 29 2023

a(13) from Michael S. Branicky, Apr 10 2023

a(14)-a(15) from Kamada data by Tyler Busby, Apr 20 2024