

A056683


Numbers n such that 40*R_n + 9 is prime, where R_n = 11...1 is the repunit (A002275).


2




OFFSET

1,1


COMMENTS

Also numbers n such that (4*10^(n+1)+41)/9 is prime.
a(11) > 10^5.  Robert Price, Nov 09 2014


LINKS

Table of n, a(n) for n=1..10.
Makoto Kamada, Prime numbers of the form 44...449.
Index entries for primes involving repunits


FORMULA

a(n) = A099414(n+1)  1.  Robert Price, Nov 09 2014


MATHEMATICA

Do[ If[ PrimeQ[40*(10^n  1)/9 + 9], Print[n]], {n, 5000}]


PROG

(MAGMA) [n: n in [0..300]  IsPrime((4*10^(n+1)+41)div 9)]; Vincenzo Librandi, Nov 10 2014


CROSSREFS

Cf. A002275, A099414.
Sequence in context: A154775 A210418 A167454 * A247963 A105288 A242915
Adjacent sequences: A056680 A056681 A056682 * A056684 A056685 A056686


KEYWORD

hard,nonn


AUTHOR

Robert G. Wilson v, Aug 10 2000


EXTENSIONS

a(8)a(10) derived from A099414 by Robert Price, Nov 09 2014


STATUS

approved



