|
|
A239926
|
|
3^(p-1)-2^(p+1) for primes p > 3.
|
|
1
|
|
|
17, 473, 54953, 515057, 42784577, 386371913, 31364282393, 22875718713137, 205886837127353, 150094360419092177, 12157661061010417697, 109418971539326314793, 8862937838177524385273, 6461081871212274789450257, 4710128696093323330314756713
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
3^(p-1)-2^(p+1) can be written as (3^((p-1)/2)-2^((p+1)/2))*(3^((p-1)/2)+2^((p+1)/2)). Since 3^((p-1)/2)-2^((p+1)/2) > 1 for p > 5, these numbers are all composite after 17 = (3^2-2^3)*(3^2+2^3).
|
|
LINKS
|
|
|
MATHEMATICA
|
Table[3^(Prime[n] - 1) - 2^(Prime[n] + 1), {n, 3, 100}]
|
|
PROG
|
(Magma) [3^(p-1)-2^(p+1): p in PrimesInInterval(4, 100)];
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,easy,less
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|