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A103059
Numbers n such that 7*10^n + 4*R_n + 5 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
1, 4, 7, 34, 82, 451, 772, 2554, 6250, 15137, 20074, 37378, 53068
OFFSET
1,2
COMMENTS
Also numbers n such that (67*10^n+41)/9 is prime.
a(14) > 10^5. - Robert Price, Sep 27 2015
FORMULA
a(n) = A101142(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(67*10^n + 41)/9], Print[n]], {n, 0, 10000}]
CROSSREFS
Sequence in context: A237424 A143547 A149090 * A123809 A140981 A283819
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 19 2005
EXTENSIONS
a(10)-a(11) from Kamada data by Robert Price, Dec 14 2010
a(12) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
a(13) from Robert Price, Sep 27 2015
STATUS
approved