OFFSET
1,1
FORMULA
a(n) = 1 + A056712(n). - Omar E. Pol, Dec 02 2017
EXAMPLE
499, 4999, 49999, 4999999 are prime, while 4, 49, 499999, 49999999 are composite.
MATHEMATICA
Select[Range[10^3], PrimeQ[10^#/2 - 1] &] (* Michael De Vlieger, Dec 02 2017 *)
PROG
(PARI) isok(n) = isprime(10^n/2 - 1); \\ Michel Marcus, Dec 02 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Patrick A. Thomas, Dec 02 2017
EXTENSIONS
a(7)-a(25) from Michel Marcus and Omar E. Pol, Dec 02 2017
STATUS
approved