|
|
A063681
|
|
Primes p such that 2p+7 is a power of three.
|
|
0
|
|
|
37, 265717, 193710241, 1270932914161, 187855106306818130162790081799568953899918191769361, 884821727139988111281341588371104523273965529248966451172919369920848760385637
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
If (3^i-7)/2 is prime then x=3^i-7 is a solution of sigma(x)+7 = sigma(x+7). See A063680 and indices resulting in primes are in A063679.
|
|
LINKS
|
|
|
FORMULA
|
2*37+7 = 3^4, so 37 is in the sequence.
|
|
MATHEMATICA
|
Select[(#-7)/2&/@(3^Range[2, 250]), PrimeQ] (* Harvey P. Dale, May 10 2014 *)
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|