A287061 Numbers k such that (10^(k+3)*6319 + 863)/9 is prime (k > 0).

11, 19, 23, 31, 73, 257, 613, 5327, 62359

Offset

1,1

Comments

The generated prime numbers are of the form '702'||...'1'...||'207' ('1' concatenated k times to which the prefix '702' and the suffix '207' are concatenated once).

a(1)..a(7) themselves are primes. a(10) > 80000, if it exists.

Links

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

Example

11 is a term as (10^(11+3)*6319 + 863)/9 = 70211111111111207 is prime.
23 is a term because (10^(23+3)*6319 + 863)/9 = 70211111111111111111111111207 is prime.

Mathematica

ParallelMap[ If[ PrimeQ[ (10^(#+3)*6319+863)/9], #, Nothing]&, Range[1000]]

Prog

(PARI) is(n) = ispseudoprime((10^(n+3)*6319+863)/9); \\ Altug Alkan, Jul 23 2017

Crossrefs

Cf. A032674, A260405, A286916.

Sequence in context: A320867 A165947 A129517 * A359401 A161601 A352480

Adjacent sequences: A287058 A287059 A287060 * A287062 A287063 A287064

Keyword

nonn,base,hard,more

Author

Mikk Heidemaa, May 19 2017

Status

approved