|
|
A293029
|
|
Numbers k such that (7*10^k - 439)/9 is prime.
|
|
0
|
|
|
2, 20, 34, 35, 65, 73, 89, 94, 103, 157, 208, 217, 430, 508, 1220, 4729, 5218, 6350, 11810, 29893, 37753, 89539, 165350
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
For k>1, numbers such that k-2 occurrences of the digit 7 followed by the digits 29 is prime (see Example section).
a(24) > 2*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
2 is in this sequence because (7*10^2 - 439)/9 = 29 is prime.
Initial terms and primes associated:
a(1) = 2, 29;
a(2) = 20, 77777777777777777729;
a(3) = 34, 7777777777777777777777777777777729;
a(4) = 35, 77777777777777777777777777777777729;
a(5) = 65, 77777777777777777777777777777777777777777777777777777777777777729; etc.
|
|
MATHEMATICA
|
Select[Range[1, 100000], PrimeQ[(4*10^# + 137)/3] &]
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|