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

1,1

Comments

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

a(12) > 10000.

Links

Table of n, a(n) for n=1..15.

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

Example

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

Mathematica

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

Prog

(Magma) [n: n in [3..700] | IsPrime(10^n-2001)];
(PARI) isok(n) = isprime(10^n - 2001); \\ Michel Marcus, Dec 03 2016

Crossrefs

Cf. similar sequences listed in A278470.

Sequence in context: A333917 A335248 A308222 * A223588 A358423 A183401

Adjacent sequences: A278468 A278469 A278470 * A278472 A278473 A278474

Keyword

nonn,more,changed

Author

Vincenzo Librandi, Nov 28 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

Status

approved