|
|
A295032
|
|
Numbers k such that 12*10^k - 7 is prime.
|
|
0
|
|
|
0, 1, 2, 4, 5, 8, 11, 21, 25, 105, 191, 305, 463, 704, 1320, 1404, 1580, 1675, 2215, 3475, 6323, 10560, 28817, 30356, 98198
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,3
|
|
COMMENTS
|
For k > 1, numbers such that the digits 11 followed by k-1 occurrences of the digit 9 followed by the digit 3 is prime (see Example section).
a(26) > 3*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
2 is in this sequence because 12*10^2 - 7 = 1193 is prime.
Initial terms and primes associated:
a(1) = 0, 5;
a(2) = 1, 113;
a(3) = 2, 1193;
a(4) = 4, 119993;
a(5) = 5, 1199993; etc.
|
|
MATHEMATICA
|
Select[Range[0, 100000], PrimeQ[12*10^# - 7 ] &]
|
|
PROG
|
(PARI) isok(k) = isprime(12*10^k - 7); \\ Michel Marcus, Nov 13 2017
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|