A111021 Integers k such that 7*10^k + 31 is a prime number.

1, 8, 11, 143, 203, 2727, 2911, 3339, 17039

Offset: 1

Author

Julien Peter Benney (jpbenney(AT)ftml.net), Oct 04 2005

Keywords

• nonn
• more

Comments

See Kamada link - primecount.txt for terms, primesize.txt for discovery details including probable or proved primes - search on "70031".

a(10) > 10^5. - Robert Price, Jan 28 2017

Examples

			k = 11 is a term because 7*10^11 + 31 = 7*100000000000 + 31 = 700000000000 + 31 = 700000000031, which is a prime.
		

Links

• Makoto Kamada, List of near-repdigit-related prime numbers.
• Index entries for primes involving repunits.

Crossrefs

Cf. A049054, A088274, A088275, A095688, A107083, A108049, A108050, A108052, A108054, A110980.

Programs

Magma

[n: n in [1..300] | IsPrime(7*10^n+31)]; // Vincenzo Librandi, Jul 03 2016

Mathematica

Select[Range[0, 10000], PrimeQ[7 10^# + 31] &] (* Vincenzo Librandi, Jul 03 2016 *)

Extensions

a(9) from Ray Chandler, Dec 23 2010

a(1) = 1 prepended by Vincenzo Librandi, Jul 03 2016