

A286916


Positive numbers n such that (10^(n+2)*331133)/9 is prime.


2




OFFSET

1,1


COMMENTS

Or '36'...'7'...'63' in decimal form is prime ('7' concatenated n times to which the prefix '36' and the suffix '63' are concatenated once).
a(1)...a(4) and a(7) themselves are primes, a(8)>50000 (if it exists).


LINKS

Table of n, a(n) for n=1..7.


EXAMPLE

a(1)=7 as 36777777763 is prime (as string, it consists '7' concatenated 7 times to which the prefix '36' and the suffix '63' are concatenated once).


MATHEMATICA

ParallelMap[ If[ PrimeQ[ (10^(#+2)*331133)/9], #, Nothing]&, Range[5000]]


PROG

(PARI) is(n)=ispseudoprime((10^(n+2)*331133)/9) \\ Charles R Greathouse IV, Jun 13 2017


CROSSREFS

Sequence in context: A316118 A265766 A228727 * A032690 A188557 A090992
Adjacent sequences: A286913 A286914 A286915 * A286917 A286918 A286919


KEYWORD

nonn,base,hard,more


AUTHOR

Mikk Heidemaa, May 17 2017


STATUS

approved



