|
|
A294910
|
|
Numbers k such that (109*10^k + 17)/9 is prime.
|
|
0
|
|
|
2, 3, 9, 23, 27, 32, 50, 80, 107, 140, 992, 1607, 2975, 4007, 4605, 12392, 15159, 16628, 37419
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
For k > 1, numbers such that the digits 12 followed by k-1 occurrences of the digit 1 followed by the digit 3 is prime (see Example section).
a(20) > 2*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
2 is in this sequence because (109*10^2 + 17)/9 = 1213 is prime.
Initial terms and primes associated:
a(1) = 2, 1213;
a(2) = 3, 12113;
a(3) = 9, 12111111113;
a(4) = 23, 1211111111111111111111113;
a(5) = 27, 12111111111111111111111111113; etc.
|
|
MATHEMATICA
|
Select[Range[0, 100000], PrimeQ[(109*10^# + 17)/9] &]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|