

A286916


Positive numbers k such that (10^(k+2)*331  133)/9 is prime.


2




OFFSET

1,1


COMMENTS

Or '36'...'7'...'63' in decimal form is prime ('7' concatenated k 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



EXAMPLE

7 is a term as 36777777763 is prime (as a string, it consists of '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



CROSSREFS



KEYWORD

nonn,hard,more,base


AUTHOR



STATUS

approved



