OFFSET
1,2
COMMENTS
Also numbers n such that 2*10^n + 9*R_n - 6 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
a(21) > 10^5. - Robert Price, Jan 25 2015
a(24) > 2*10^5. - Robert Price, Aug 09 2015
LINKS
FORMULA
a(n) = A101973(n) + 1.
EXAMPLE
For n=1,2,5 the corresponding primes are 23,293,29993.
MATHEMATICA
Do[ If[ PrimeQ[3*10^n-7], Print[n]], {n, 0, 10000}]
PROG
(PARI) is_ok(n)=isprime(3*10^n-7); /* Anders Hellström, Aug 09 2015 */
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 17 2004
EXTENSIONS
Addition of a(12)-a(15) from Kamada data by Robert Price, Dec 12 2010
a(16)-a(20) from Kamada data by Robert Price, Jan 25 2015
a(21)-a(23) from Robert Price, Aug 09 2015
STATUS
approved