|
|
A282505
|
|
Numbers k such that (5*10^k - 29)/3 is prime.
|
|
0
|
|
|
1, 2, 3, 4, 5, 6, 12, 32, 63, 116, 154, 221, 267, 468, 605, 749, 1911, 7241, 7406, 7797, 9428, 11094, 43917, 44127, 58384, 131223, 181127
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
For k>1, numbers such that the digit 1 followed by k-2 occurrences of the digit 6 followed by the digits 57 is prime (see Example section).
a(28) > 2*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
3 is in this sequence because (5*10^3 - 29)/3 = 1657 is prime.
Initial terms and primes associated:
a(1) = 1, 7;
a(2) = 2, 157;
a(3) = 3, 1657;
a(4) = 4, 16657;
a(5) = 5, 166657; etc.
|
|
MATHEMATICA
|
Select[Range[1, 100000], PrimeQ[(5*10^# - 29)/3] &]
|
|
PROG
|
(PARI) isok(k) = isprime((5*10^k - 29)/3); \\ Michel Marcus, Mar 06 2018
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|