|
|
A282457
|
|
Numbers k such that 7*10^k - 47 is prime.
|
|
0
|
|
|
1, 2, 5, 8, 11, 14, 15, 30, 31, 42, 69, 85, 120, 128, 449, 685, 686, 741, 1291, 1521, 2165, 9110, 9150, 11366, 13154, 33321, 40758, 50789, 51440, 65492, 82509, 93887, 266024
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
For k>1, numbers such that the digit 6 followed by k-2 occurrences of the digit 9 followed by the digits 53 is prime (see Example section).
a(34) > 3*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
2 is in this sequence because 7*10^2 - 47 = 653 is prime.
Initial terms and primes associated:
a(1) = 1, 23;
a(2) = 2, 653;
a(3) = 5, 699953;
a(4) = 8, 699999953;
a(5) = 11, 699999999953; etc.
|
|
MATHEMATICA
|
Select[Range[1, 100000], PrimeQ[7*10^# - 47] &]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
Reordered terms into ascending order by Robert Price, Apr 01 2022
|
|
STATUS
|
approved
|
|
|
|