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

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

Offset

1,2

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

Links

Table of n, a(n) for n=1..9.

Makoto Kamada, List of near-repdigit-related prime numbers.

Index entries for primes involving repunits.

Example

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

Mathematica

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

Prog

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

Crossrefs

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

Sequence in context: A196173 A074042 A140478 * A126814 A172391 A227239

Adjacent sequences: A111018 A111019 A111020 * A111022 A111023 A111024

Keyword

nonn,more

Author

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

Extensions

a(9) from Ray Chandler, Dec 23 2010

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

Status

approved