|
|
A096507
|
|
Numbers k such that 6*R_k + 1 is a prime, where R_k = 11...1 is the repunit (A002275) of length k.
|
|
13
|
|
|
1, 2, 6, 8, 9, 11, 20, 23, 41, 63, 66, 119, 122, 149, 252, 284, 305, 592, 746, 875, 1204, 1364, 2240, 2403, 5106, 5776, 5813, 12456, 14235, 39606, 55544, 84239, 275922
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
Also numbers k such that (2*10^k + 1)/3 is prime.
These numbers form a near-repdigit sequence (6)w7.
All the terms from k = 2403 through 14235 correspond to primes. - Joao da Silva (zxawyh66(AT)yahoo.com), Oct 03 2005
|
|
LINKS
|
|
|
FORMULA
|
|
|
EXAMPLE
|
k = 9 gives 2000000001/3 = 666666667, which is prime.
k = 20 gives 66666666666666666667, which is prime.
|
|
MATHEMATICA
|
Select[Range@ 2500, PrimeQ[FromDigits@ Table[6, {#}] + 1] &] (* or *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,changed
|
|
AUTHOR
|
|
|
EXTENSIONS
|
More terms from Julien Peter Benney (jpbenney(AT)ftml.net), Sep 14 2004
|
|
STATUS
|
approved
|
|
|
|