|
| |
|
|
A056688
|
|
Numbers n such that 70*R_n + 1 is prime, where R_n = 11...1 is the repunit (A002275) of length n.
|
|
2
|
|
|
|
1, 12, 19, 22, 30, 99, 240, 274, 924, 1066, 1368, 2064, 7162, 37962, 91855, 111705, 260197, 271756
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,2
|
|
|
COMMENTS
|
Also numbers n such that (7*10^(n+1)-61)/9 is prime.
|
|
|
LINKS
|
Table of n, a(n) for n=1..18.
Makoto Kamada, Prime numbers of the form 77...771.
Index entries for primes involving repunits
|
|
|
FORMULA
|
a(n) = A099419(n) - 1.
|
|
|
MATHEMATICA
|
Do[ If[ PrimeQ[70*(10^n - 1)/9 + 1], Print[n]], {n, 0, 7000}]
|
|
|
CROSSREFS
|
Cf. A093176.
Sequence in context: A112880 A211083 A100541 * A107911 A143800 A003335
Adjacent sequences: A056685 A056686 A056687 * A056689 A056690 A056691
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Robert G. Wilson v, Aug 10 2000
|
|
|
EXTENSIONS
|
a(13) from Kamada link by Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 01 2008
a(14)-a(15) from Erik Branger, Dec 19 2009
a(16) from Erik Branger, Jan 29 2011
a(17) from Erik Branger, Nov 26 2011
a(18) from Erik Branger, Mar 05 2012
|
|
|
STATUS
|
approved
|
| |
|
|
