|
| |
|
|
A294125
|
|
Numbers k such that (412*10^k - 7)/9 is prime.
|
|
0
|
|
|
|
1, 16, 22, 26, 29, 55, 83, 110, 128, 176, 187, 566, 1150, 1405, 3515, 7763, 14530, 18398, 26035, 42166, 85897
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,2
|
|
|
COMMENTS
|
For k>1, numbers such that the digits 45 followed by k occurrences of the digit 7 is prime (see Example section).
a(22) > 10^5.
|
|
|
LINKS
|
Table of n, a(n) for n=1..21.
Makoto Kamada, Factorization of near-repdigit-related numbers.
Makoto Kamada, Search for 457w
|
|
|
EXAMPLE
|
1 is in this sequence because (412*10^1 - 7)/9 = 457 is prime.
Initial terms and primes associated:
a(1) = 1, 457;
a(2) = 16, 457777777777777777;
a(3) = 22, 457777777777777777777777;
a(4) = 26, 4577777777777777777777777777;
a(5) = 29, 4577777777777777777777777777777; etc.
|
|
|
MATHEMATICA
|
Select[Range[0, 100000], PrimeQ[(412*10^# - 7)/9] &]
|
|
|
CROSSREFS
|
Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269.
Sequence in context: A305944 A243972 A091118 * A064804 A102944 A058901
Adjacent sequences: A294122 A294123 A294124 * A294126 A294127 A294128
|
|
|
KEYWORD
|
nonn,more,hard
|
|
|
AUTHOR
|
Robert Price, Oct 23 2017
|
|
|
STATUS
|
approved
|
| |
|
|
