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A102964
Numbers n such that 3*10^n-7 is prime.
2
1, 2, 5, 10, 29, 39, 114, 484, 865, 4180, 5385, 13122, 13832, 22676, 25020, 30057, 35910, 37935, 42295, 50194, 110076, 184124, 191152
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
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
Sequence in context: A287963 A006401 A283460 * A075885 A018377 A056363
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