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URL: https://oeis.org/A103002

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A103002
Numbers k such that 5*10^k - 7 is prime.
2
1, 3, 4, 8, 14, 16, 24, 61, 80, 87, 104, 108, 144, 2157, 3325, 4122, 20718, 51163, 140744
OFFSET
1,2
COMMENTS
Also numbers k such that 4*10^k + 9*R_k - 6 is prime, where R_k = 11...1 is the repunit (A002275) of length k.
a(20) > 2*10^5. - Robert Price, Sep 15 2015
FORMULA
a(n) = A101739(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[5*10^n - 7], Print[n]], {n, 0, 10000}]
PROG
(PARI) is(n)=ispseudoprime(5*10^n-7) \\ Charles R Greathouse IV, Jun 06 2017
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 17 2005
EXTENSIONS
a(17)-a(18) from Kamada data added by Robert Price, Dec 10 2010
a(19) from Robert Price, Sep 15 2015
STATUS
approved