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A103102
Numbers n such that 9*10^n + 5*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
0, 1, 7, 67, 127, 2107, 10003, 13741, 41523
OFFSET
1,3
COMMENTS
Also numbers n such that (86*10^n+13)/9 is prime.
a(10) > 10^5. - Robert Price, Nov 10 2015
FORMULA
a(n) = A101011(n-1) + 1, for n>1.
MATHEMATICA
Do[ If[ PrimeQ[(86*10^n + 13)/9], Print[n]], {n, 0, 10000}]
PROG
(PARI) is(n)=isprime(9*10^n + 5*((10^n-1)/9) + 2) \\ Anders Hellström, Nov 10 2015
CROSSREFS
Sequence in context: A261184 A142786 A139783 * A139910 A250227 A250275
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 19 2005
EXTENSIONS
a(7)-a(8) from Kamada data by Robert Price, Dec 14 2010
a(9) from Erik Branger May 01 2013 by Ray Chandler, Aug 17 2013
Inserted a(1)=0 by Robert Price, Nov 10 2015
STATUS
approved