|
|
A291611
|
|
Numbers k such that 5*10^k + 81 is prime.
|
|
1
|
|
|
1, 3, 6, 16, 30, 33, 36, 37, 85, 288, 561, 805, 850, 1057, 1192, 1312, 2571, 4579, 5223, 5940, 10191, 18756, 24564, 29595, 43891, 65905, 89118, 97963, 112003, 139945, 174101, 195221
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 81 is prime (see Example section).
a(33) > 2*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
3 is in this sequence because 5*10^3 + 81 = 5081 is prime.
Initial terms and primes associated:
a(1) = 1, 131;
a(2) = 3, 5081;
a(3) = 6, 5000081;
a(4) = 16, 50000000000000081;
a(5) = 30, 5000000000000000000000000000081; etc.
|
|
MATHEMATICA
|
Select[Range[0, 100000], PrimeQ[5*10^# + 81] &]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
Terms reordered into ascending order by Robert Price, Apr 03 2022
|
|
STATUS
|
approved
|
|
|
|