OFFSET
1,3
COMMENTS
Also numbers k such that (10^k + 17)/9 is prime.
The corresponding values R_k + 2 are primes of the form "(n-1) ones followed by a three"; zero is a degenerate case. Related to the base-10 repunit primes.
a(15) > 10^5. - Robert Price, Oct 12 2014
By Kamada link, a(15) > 4*10^5. - Jeppe Stig Nielsen, Jan 17 2023
LINKS
Makoto Kamada, Prime numbers of the form 11...113.
Henri Lifchitz and Renaud Lifchitz, PRP Top, Search output for (10^k+17)/9
FORMULA
a(n) = A056654(n-1) + 1.
EXAMPLE
11113 = ((10^5)+17)/9 and 11113 is prime.
MAPLE
A097683:=n->`if`((10^n+17 mod 9) = 0 and isprime(floor((10^n+17)/9)), n, NULL): seq(A097683(n), n=0..10^3); # Wesley Ivan Hurt, Oct 12 2014
MATHEMATICA
Do[ If[ PrimeQ[(10^n - 1)/9 + 2], Print[n]], {n, 0, 5951}] (* Robert G. Wilson v, Oct 15 2004 *)
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Carl R. White and Julien Peter Benney (jpbenney(AT)ftml.net), Aug 19 2004
EXTENSIONS
a(11)-a(12) from Robert G. Wilson v, Oct 15 2004
Edited by N. J. A. Sloane, Apr 02 2009, at the suggestion of Farideh Firoozbakht
a(13) from Kamada link by Ray Chandler, Dec 23 2010
a(14) from Robert Price, Oct 12 2014
STATUS
approved