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A103083
Numbers n such that 8*10^n + 5*R_n - 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
1
21, 27, 60, 471, 1074, 5781
OFFSET
1,1
COMMENTS
Also numbers n such that (77*10^n-41)/9 is prime.
a(7) > 10^5. - Robert Price, Oct 21 2015
It appears that all terms are divisible by 3. - Robert Price, Oct 21 2015
FORMULA
a(n) = A101070(n) + 1.
MATHEMATICA
Do[ If[ PrimeQ[(77*10^n - 41)/9], Print[n]], {n, 0, 10000}]
PROG
(PARI) for(n=1, 1e4, if(isprime((77*10^n-41)/9), print1(n, ", "))) \\ Altug Alkan, Oct 21 2015
CROSSREFS
Sequence in context: A098768 A208157 A114168 * A120735 A009727 A337702
KEYWORD
more,nonn
AUTHOR
Robert G. Wilson v, Jan 19 2005
STATUS
approved