A176087 Numbers n such that (10^n-1)/3 * 10^ceiling(log_10(n+1)) + n is prime.

1, 253, 35473

Offset: 1

Author

Rick L. Shepherd, Apr 08 2010

Keywords

• bref
• more
• nonn

Comments

No term is a multiple of 2, 3, or 5. The decimal expansion of each corresponding prime is n 3's with n's decimal expansion concatenated. Probable primes found by PrimeForm. Prime for 253 proved by Primo. No more terms up to 50000.

Examples

			The first term is 1 because 31 is prime.
		

Crossrefs

Cf. A070746 (n 1's followed by n is prime), A084428 (n 7's followed by n is prime), A174710, A004218.

Programs

PARI

is(n)=ispseudoprime((10^n-1)/3 * 10^logint(10*n,10) + n) \\ Charles R Greathouse IV, May 22 2017