A176091 Numbers n such that (10^n-1) * 10^ceiling(log_10(n+1)) + n is prime.

307, 1759, 2963, 3881

Offset

1,1

Comments

No term is a multiple of 2, 3, or 5. (In fact, a(1) through a(4) are prime.) The decimal expansion of each corresponding prime is n 9's with n's decimal expansion concatenated. Probable primes found by PrimeForm. Primes for 307 and 1759 proved by Primo. No more terms up to 30000.

Links

Table of n, a(n) for n=1..4.

Crossrefs

Cf. A174352 (n followed by n 9's is prime), n k's followed by n is prime: A070746 (k=1), A176087 (k=3), A176089 (k=4), A176090 (k=6), A084428 (k=7). [k=2, 5, and 8 produce only composites divisible by 3.]

Sequence in context: A308785 A142572 A204477 * A359640 A118284 A234030

Adjacent sequences: A176088 A176089 A176090 * A176092 A176093 A176094

Keyword

more,nonn

Author

Rick L. Shepherd, Apr 16 2010

Status

approved