A102964 Numbers n such that 3*10^n-7 is prime.

1, 2, 5, 10, 29, 39, 114, 484, 865, 4180, 5385, 13122, 13832, 22676, 25020, 30057, 35910, 37935, 42295, 50194, 110076, 184124, 191152

Offset: 1

Author

Robert G. Wilson v, Dec 17 2004

Keywords

• more
• nonn

Comments

Also numbers n such that 2*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.

a(21) > 10^5. - Robert Price, Jan 25 2015

a(24) > 2*10^5. - Robert Price, Aug 09 2015

Examples

			For n=1,2,5 the corresponding primes are 23,293,29993.
		

Links

• Makoto Kamada, Prime numbers of the form 299...993.
• Index entries for primes involving repunits.

Crossrefs

Cf. A002275, A101973.

Programs

Mathematica

Do[ If[ PrimeQ[3*10^n-7], Print[n]], {n, 0, 10000}]

PARI

is_ok(n)=isprime(3*10^n-7); /* Anders Hellström, Aug 09 2015 */

Formula

a(n) = A101973(n) + 1.

Extensions

Addition of a(12)-a(15) from Kamada data by Robert Price, Dec 12 2010

a(16)-a(20) from Kamada data by Robert Price, Jan 25 2015

a(21)-a(23) from Robert Price, Aug 09 2015