|
|
A291868
|
|
Numbers k such that (47*10^k - 119)/9 is prime.
|
|
0
|
|
|
2, 3, 9, 15, 39, 45, 59, 137, 180, 224, 264, 476, 491, 504, 1905, 3144, 4784, 10893, 24483, 28602, 82706, 100283, 129789, 131886, 132125
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 2 followed by the digits 09 is prime (see Example section).
a(26) > 2*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
3 is in this sequence because (47*10^3 - 119)/9 = 5209 is prime.
Initial terms and primes associated:
a(1) = 2, 509;
a(2) = 3, 5209;
a(3) = 9, 5222222209;
a(4) = 15, 5222222222222209;
a(5) = 39, 5222222222222222222222222222222222222209; etc.
|
|
MATHEMATICA
|
Select[Range[1, 100000], PrimeQ[(47*10^# - 119)/9] &]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|