A176087 -id:A176087 - cp's OEIS frontend

A176090 Numbers n such that 2(10^n-1)/3 * 10^ceiling(log_10(n+1)) + n is prime.

1, 7, 41, 2429

Offset: 1

Rick L. Shepherd, Apr 13 2010

No term is a multiple of 2, 3, or 5. The decimal expansion of each corresponding prime (in A176272) is n 6's with n's decimal expansion concatenated. Primes and probable primes found by PrimeForm. Prime for 41 proved by Primo. No more terms up to 30000.

			The numbers 1 and 7 are terms because 61 and 66666667 are prime.

Cf. A176272 (corresponding primes), n k's followed by n is prime: A070746 (k=1), A176087 (k=3), A176089 (k=4), A084428 (k=7), A176091 (k=9). [k=2, 5, and 8 produce only composites divisible by 3.]

is(n)=ispseudoprime(2*(10^n-1)/3 * 10^logint(10*n,10) + n) \\ Charles R Greathouse IV, May 22 2017

A176089 Numbers n such that 4(10^n-1)/9 * 10^ceiling(log_10(n+1)) + n is prime.

Original entry on oeis.org

1, 547, 1187, 11183

Offset: 1

Rick L. Shepherd, Apr 11 2010

No term is a multiple of 2, 3, or 5. The decimal expansion of each corresponding prime is n 4's with n's decimal expansion concatenated. Probable primes found by PrimeForm. Primes for 547 and 1187 proved by Primo. No more terms up to 30000.

			The first term is 1 because 41 is prime.

Cf. n k's followed by n is prime: A070746 (k=1), A176087 (k=3), A176090 (k=6), A084428 (k=7), A176091 (k=9). [k=2, 5, and 8 produce only composites divisible by 3.]

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

Original entry on oeis.org

307, 1759, 2963, 3881

Offset: 1

Rick L. Shepherd, Apr 16 2010

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.

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.]

cp's OEIS Frontend

A176090 Numbers n such that 2(10^n-1)/3 * 10^ceiling(log_10(n+1)) + n is prime.

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A176089 Numbers n such that 4(10^n-1)/9 * 10^ceiling(log_10(n+1)) + n is prime.

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

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