A174710 Numbers k such that k*10^k + (10^k - 1)/3 is prime.

1, 2, 275, 1556, 36682

Offset: 1

Author

Rick L. Shepherd, Mar 27 2010

Keywords

• more
• nonn

Comments

No term is a multiple of 3. The decimal expansion of each corresponding prime is n's decimal expansion with n 3's concatenated. Primes and probable primes found by PrimeForm. Primes for 275 and 1556 proved by Primo. No more terms up to 30000.

No more terms up to 50000. - Michael S. Branicky, Oct 11 2024

Examples

			The numbers 1 and 2 are terms because 13 and 233 are prime.
		

Crossrefs

Cf. A068817 (n followed by n 1's is prime), A133127 (n followed by n 7's is prime), A174352 (n followed by n 9's is prime).

Programs

PARI

is(n)=ispseudoprime(n*10^n+(10^n-1)/3) \\ Charles R Greathouse IV, Jun 13 2017

Extensions

a(5) from Michael S. Branicky, Oct 11 2024