OFFSET
1,1
COMMENTS
Also numbers k such that 10^k - 9 is a prime.
LINKS
FORMULA
a(n) = A056696(n) + 1.
EXAMPLE
a(2) = 5, since 10^5 - 9 = 99991, which is prime.
MATHEMATICA
Do[ If[ PrimeQ[10^n - 9], Print[n]], {n, 0, 7000}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Alonso del Arte, Jul 07 2004
EXTENSIONS
a(12) - a(14) from Robert G. Wilson v, Oct 15 2004
a(15) - a(16) from Jason Earls, Jan 07 2008
a(17) - a(19) from Alexander Gramolin, May 13 2011
Edited by Ray Chandler, Feb 26 2012
Title corrected by Robert Price, Sep 06 2014
STATUS
approved