OFFSET
1,1
COMMENTS
a(5) produces the prime: 4182...[4183 times]4183 (16736 digits).
EXAMPLE
7 occurs because '6' prepended 7 times to '7' produces prime (66666667).
MATHEMATICA
Select[ Range[1200], PrimeQ[ FromDigits[ StringJoin@@ ToString/@ PadLeft[{#}, #+1, #-1]]] &]
CROSSREFS
KEYWORD
nonn,more,hard
AUTHOR
Mikk Heidemaa, Jan 12 2016
STATUS
approved