

A056695


Numbers n such that 80*R_n + 7 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


2



0, 2, 3, 5, 8, 11, 71, 117, 123, 189, 243, 303, 356, 1421, 2690, 5537, 7580, 21905, 32175, 44357
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OFFSET

1,2


COMMENTS

Also numbers n such that (8*10^(n+1)17)/9 is prime.
a(21) > 10^5.  Robert Price, May 20 2014


LINKS

Table of n, a(n) for n=1..20.
Makoto Kamada, Prime numbers of the form 88...887.
Index entries for primes involving repunits


FORMULA

a(n) = A096846(n)  1.


MATHEMATICA

Do[ If[ PrimeQ[80*(10^n  1)/9 + 7], Print[n]], {n, 0, 5000}]


CROSSREFS

Cf. A002275, A093171, A096846.
Sequence in context: A259973 A092362 A105766 * A287006 A020899 A057987
Adjacent sequences: A056692 A056693 A056694 * A056696 A056697 A056698


KEYWORD

hard,nonn,more


AUTHOR

Robert G. Wilson v, Aug 10 2000


EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(18)a(20) derived from A096846 by Robert Price, May 20 2014


STATUS

approved



