OFFSET
1,2
COMMENTS
Also numbers k such that (7*10^(k+1)-61)/9 is prime.
LINKS
FORMULA
a(n) = A099419(n) - 1.
MATHEMATICA
Do[ If[ PrimeQ[70*(10^n - 1)/9 + 1], Print[n]], {n, 0, 7000}]
CROSSREFS
KEYWORD
nonn
AUTHOR
Robert G. Wilson v, Aug 10 2000
EXTENSIONS
a(13) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(14)-a(15) from Erik Branger, Dec 19 2009
a(16) from Erik Branger, Jan 29 2011
a(17) from Erik Branger, Nov 26 2011
a(18) from Erik Branger, Mar 05 2012
a(19)-a(20) from Erik Branger, Sep 23 2016
STATUS
approved