|
|
A278426
|
|
Numbers n such that (26*10^n - 89) / 9 is prime.
|
|
0
|
|
|
1, 3, 4, 13, 15, 21, 27, 63, 70, 123, 136, 178, 208, 265, 411, 457, 856, 2401, 4642, 8017, 8211, 8385, 12337, 20793, 123970, 189928
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,2
|
|
COMMENTS
|
For n>1, numbers such that the digit 2 followed by n-2 occurrences of the digit 8 followed by the digits 79 is prime (see Example section).
a(27) > 2*10^5.
|
|
LINKS
|
|
|
EXAMPLE
|
4 is in this sequence because (26*10^4 - 89) / 9 = 28879 is prime.
Initial terms and primes associated:
a(1) = 1, 19;
a(2) = 3, 2879;
a(3) = 4, 28879;
a(4) = 13, 28888888888879;
a(5) = 15, 2888888888888879; etc.
|
|
MATHEMATICA
|
Select[Range[0, 100000], PrimeQ[(26*10^# - 89) / 9] &]
|
|
PROG
|
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,more,hard
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|