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A103074
Numbers n such that 8*10^n + 2*R_n - 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
0, 2, 3, 5, 17, 47, 177, 8462, 36615
OFFSET
1,2
COMMENTS
Also numbers n such that (74*10^n-11)/9 is prime.
a(10) > 10^5. - Robert Price, Oct 13 2015
FORMULA
a(n) = A101061(n-1) + 1 for n>1.
MATHEMATICA
Do[ If[ PrimeQ[(74*10^n - 11)/9], Print[n]], {n, 0, 10000}]
PROG
(PARI) for(n=0, 50000, if(isprime((74*10^n-11)/9), print1(n", "))) \\ Altug Alkan, Oct 13 2015
CROSSREFS
Sequence in context: A235630 A235636 A268130 * A173236 A268209 A245641
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 19 2005
EXTENSIONS
a(9) from Erik Branger May 01 2013 by Ray Chandler, Aug 16 2013
Inserted a(1)=0 by Robert Price, Oct 13 2015
STATUS
approved