|
|
A280632
|
|
Numbers k such that (19*10^k + 191)/3 is prime.
|
|
0
|
|
|
1, 3, 4, 9, 10, 11, 14, 25, 38, 74, 110, 133, 145, 469, 1035, 1808, 3323, 4534, 4875, 5306, 16645, 20591, 25904, 29365, 81488, 108184, 132550
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
For k > 1, numbers k such that the digit 6 followed by k-2 occurrences of the digit 3 followed by the digits 97 is prime (see Example section).
a(28) > 2*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
4 is in this sequence because (19*10^4 + 191) / 3 = 63397 is prime.
Initial terms and associated primes:
a(1) = 1, 127;
a(2) = 3, 6397;
a(3) = 4, 63397;
a(4) = 9, 6333333397;
a(5) = 10, 63333333397; etc.
|
|
MATHEMATICA
|
Select[Range[0, 100000], PrimeQ[(19*10^# + 191) / 3] &]
|
|
PROG
|
(PARI) isok(n) = isprime((19*10^n + 191)/3); \\ Michel Marcus, Jan 07 2017
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|