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

1, 253, 35473

Offset

1,2

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.

Links

Table of n, a(n) for n=1..3.

Example

The first term is 1 because 31 is prime.

Prog

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

Crossrefs

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

Sequence in context: A242463 A271985 A255182 * A006060 A077695 A253880

Adjacent sequences: A176084 A176085 A176086 * A176088 A176089 A176090

Keyword

bref,more,nonn

Author

Rick L. Shepherd, Apr 08 2010

Status

approved