OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..2500
EXAMPLE
910109 is prime and of the form 9nn9 for n=10.
9101310139 is prime and of the form 9nn9 for n=1013.
MATHEMATICA
Select[Table[FromDigits[Join[{9}, IntegerDigits[n], IntegerDigits[n], {9}]], {n, 1100}], PrimeQ] (* Harvey P. Dale, Jul 28 2020 *)
CROSSREFS
KEYWORD
easy,nonn,base
AUTHOR
Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005
STATUS
approved