OFFSET
1,2
COMMENTS
For k > 2, numbers such that '37'||...'6'...||'73' ('6' concatenated k-2 times and prefixed by '37', and suffixed by '73') in decimal form is prime.
EXAMPLE
13 is in the sequence because (10^13*113 + 19)/3 = 376666666666673 is prime.
MATHEMATICA
ParallelTable[ If[ PrimeQ[ (10^n*113+19)/3], n, Nothing], {n, 2000}]
PROG
(PARI) isok(n) = isprime((10^n*113 + 19)/3); \\ Michel Marcus, Jul 21 2017
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Mikk Heidemaa, May 31 2017
STATUS
approved