OFFSET
1,2
COMMENTS
Also numbers k such that (13*10^k - 1)/3 is prime.
a(24) > 10^5. - Robert Price, Dec 21 2014
LINKS
EXAMPLE
43 and 433 are prime, so 1 and 2 are terms of the sequence.
MATHEMATICA
Do[ If[ PrimeQ[ 4*10^n + 3*(10^n-1)/9], Print[n]], {n, 0, 5000}]
CROSSREFS
KEYWORD
hard,nonn
AUTHOR
Robert G. Wilson v, Aug 10 2000
EXTENSIONS
26044 from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(18)-a(23) from Robert Price, Dec 21 2014
STATUS
approved