

A099418


Numbers n such that 5*R_n + 4 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


3



2, 8, 12, 18, 26, 32, 138, 188, 222, 338, 1002, 2744, 6530, 38690, 39464
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,1


COMMENTS

Also numbers n such that (5*10^n+31)/9 is prime.


LINKS

Table of n, a(n) for n=1..15.
Makoto Kamada, Prime numbers of the form 55...559.
Index entries for primes involving repunits


FORMULA

a(n) = A056687(n) + 1.


MATHEMATICA

Do[ If[ PrimeQ[ 5(10^n  1)/9 + 4], Print[n]], {n, 0, 5000}]


CROSSREFS

Cf. A002275, A093403, A056687.
Sequence in context: A046525 A235353 A057265 * A108987 A035405 A280867
Adjacent sequences: A099415 A099416 A099417 * A099419 A099420 A099421


KEYWORD

nonn


AUTHOR

Robert G. Wilson v, Oct 14 2004


EXTENSIONS

a(13)a(15) from Kamada link by Ray Chandler, Feb 27 2012


STATUS

approved



