

A102945


Numbers n such that 10^n + 8*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.


3




OFFSET

1,2


COMMENTS

Also numbers n such that (17*10^n+1)/9 is prime.
No more terms below 133000. [Serge Batalov, May 15 2010]
a(11) > 2*10^5.  Robert Price, Nov 16 2014


LINKS

Table of n, a(n) for n=1..10.
Makoto Kamada, Prime numbers of the form 188...889.
Index entries for primes involving repunits.


FORMULA

a(n) = A102031(n) + 1.


MAPLE

A102945:=n>`if`(isprime((17*10^n+1)/9), n, NULL): seq(A102945(n), n=1..10^3); # Wesley Ivan Hurt, Nov 16 2014


MATHEMATICA

Do[ If[ PrimeQ[(17*10^n + 1)/9], Print[n]], {n, 0, 10000}]
Select[Range[1000], PrimeQ[(17 10^# + 1) / 9] &] (* Vincenzo Librandi, Nov 17 2014 *)


PROG

(MAGMA) [n: n in [0..300]  IsPrime((17*10^n+1) div 9)]; // Vincenzo Librandi, Nov 17 2014


CROSSREFS

Cf. A002275, A102031.
Sequence in context: A321603 A297564 A280086 * A300532 A249940 A132515
Adjacent sequences: A102942 A102943 A102944 * A102946 A102947 A102948


KEYWORD

more,nonn


AUTHOR

Robert G. Wilson v, Dec 16 2004


EXTENSIONS

More PRP terms a(7)a(10). Sieved with srsieve and tested with Prime95 by Serge Batalov, May 15 2010


STATUS

approved



