|
|
A273542
|
|
Numbers k such that (238*10^k - 1)/3 is prime.
|
|
0
|
|
|
0, 2, 3, 4, 6, 10, 12, 38, 40, 47, 59, 76, 131, 154, 227, 404, 762, 782, 987, 993, 3449, 5692, 10086, 11630, 15135, 26384, 28233, 33179, 48352, 103210, 118265, 145276, 151979, 209715, 210712
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
For k > 1, numbers k such that the digits 79 followed by k occurrences of the digit 3 is prime (see Example section).
a(36) > 3*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
3 is in this sequence because (238*10^3-1)/3 = 79333 is prime.
Initial terms and associated primes:
a(1) = 0, 79;
a(2) = 2, 7933;
a(3) = 3, 79333;
a(4) = 4, 793333;
a(5) = 6, 79333333, etc.
|
|
MATHEMATICA
|
Select[Range[0, 100000], PrimeQ[(238*10^# - 1)/3] &]
|
|
PROG
|
(Magma) [n: n in [0..500] | IsPrime((238*10^n - 1) div 3)]; // Vincenzo Librandi, May 25 2016
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|