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URL: https://oeis.org/A102978

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A102978
Numbers k such that 3*10^k + 8*R_k - 7 is a prime, where R_k = 11...1 is the repunit (A002275) of length k.
2
1, 3, 19, 30, 40, 42, 45, 70, 307, 538, 1609, 1668, 1674, 4492, 4935, 6112, 12819, 14079, 16020, 23005, 50997, 82870
OFFSET
1,2
COMMENTS
Also numbers k such that (35*10^k-71)/9 is a prime.
a(23) > 10^5. - Robert Price, May 20 2015
FORMULA
a(n) = A101844(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(35*10^n - 71)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A108137 A250027 A339545 * A218537 A236969 A222590
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Dec 17 2004
EXTENSIONS
Addition of a(17)-a(20) from Kamada data by Robert Price, Dec 10 2010
a(21)-a(22) from Robert Price, May 20 2015
STATUS
approved