|
| |
|
|
A098089
|
|
Numbers n such that 7*R_n + 2 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
|
|
0
| | |
|
|
|
OFFSET
| 1,1
|
|
|
COMMENTS
| Also numbers n such that (7*10^n+11)/9 is prime.
|
|
|
LINKS
| Makoto Kamada, Factorizations of 77...779.
Index entries for primes involving repunits
|
|
|
EXAMPLE
| If n = 2, we get ((7*10^2)+11/9 = (700+11)/9 = 79, which is prime.
|
|
|
MATHEMATICA
| Do[ If[ PrimeQ[ 7(10^n - 1)/9 + 2], Print[n]], {n, 5000}] (from Robert G. Wilson v Oct 15 2004)
Do[ If[ PrimeQ[((7*10^n) + 11)/9], Print[n]], {n, 8131}] (from Robert G. Wilson v Sep 27 2004)
|
|
|
CROSSREFS
| Equals 1+A056693(n).
Sequence in context: A198665 A003821 A055765 * A075809 A131472 A098532
Adjacent sequences: A098086 A098087 A098088 * A098090 A098091 A098092
|
|
|
KEYWORD
| more,nonn
|
|
|
AUTHOR
| Julien Peter Benney (jpbenney(AT)ftml.net), Sep 14 2004
|
|
|
EXTENSIONS
| a(9) from Kamada link by Ray Chandler (rayjchandler(AT)sbcglobal.net), Dec 23 2010
|
| |
|
|
