|
|
A250291
|
|
Numbers n such that (2^n+1)/3 is a semiprime.
|
|
1
|
|
|
29, 37, 41, 47, 49, 53, 67, 71, 73, 103, 107, 109, 139, 151, 179, 223, 229, 251, 269, 277, 311, 349, 353, 433, 457, 487, 503, 599, 601, 613, 619, 643, 739, 757, 827, 839, 1031, 1061, 1117
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
First unknown: 1123.
If (2^n+1)/3 is a semiprime, n must be prime or the square of a prime; the only known square of a prime in this sequence is 49.
|
|
LINKS
|
|
|
EXAMPLE
|
a(1) = 29 so (2^29+1)/3 = 178956971 = 59 * 3033169 is a semiprime.
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|