|
|
A287208
|
|
Numbers k such that 8*10^k - 13 is prime.
|
|
0
|
|
|
1, 2, 4, 7, 8, 13, 23, 28, 37, 40, 107, 132, 156, 290, 295, 653, 948, 2292, 4727, 6188, 7340, 24326, 34031, 41026, 66848, 104893, 106157, 125088, 230921, 295160
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
For k>1, numbers such that the digit 7 followed by k-2 occurrences of the digit 9 followed by the digits 87 is prime (see Example section).
a(31) > 3*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
4 is in this sequence because 8*10^4 - 13 = 79987 is prime.
Initial terms and primes associated:
a(1) = 1, 67;
a(2) = 2, 787;
a(3) = 4, 79987;
a(4) = 7, 79999987;
a(5) = 8, 799999987; etc.
|
|
MATHEMATICA
|
Select[Range[1, 100000], PrimeQ[8*10^# - 13] &]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|