|
| |
|
|
A109080
|
|
Numbers n such that 5^n - 2 is prime.
|
|
18
|
|
|
|
1, 2, 14, 26, 50, 126, 144, 260, 624, 1424, 10472, 19784, 24558, 797390
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,2
|
|
|
COMMENTS
|
No more terms through 18000.
No more terms through 50000. - Ryan Propper, Dec 10 2008
a(14) > 10^5. - Robert Price, Feb 03 2014
a(14) > 185000. - Tyler NeSmith, Dec 13 2020
Searched 185000 to 800000. - Paul Bourdelais, Mar 03 2021
|
|
|
LINKS
|
Table of n, a(n) for n=1..14.
F. Firoozbakht, M. F. Hasler, Variations on Euclid's formula for Perfect Numbers, JIS 13 (2010) #10.3.1
|
|
|
EXAMPLE
|
5^14 - 2 = 6103515623 is prime, hence 14 is in the sequence.
|
|
|
MATHEMATICA
|
Do[If[PrimeQ[5^n - 2], Print[n]], {n, 1, 18000}]
|
|
|
PROG
|
(PARI) for(n=1, 10^5, if(ispseudoprime(5^n-2), print1(n, ", "))) \\ Felix Fröhlich, Jun 05 2014
|
|
|
CROSSREFS
|
Sequence in context: A194411 A017545 A280268 * A295083 A180877 A032461
Adjacent sequences: A109077 A109078 A109079 * A109081 A109082 A109083
|
|
|
KEYWORD
|
hard,nonn
|
|
|
AUTHOR
|
Ryan Propper, Jun 18 2005
|
|
|
EXTENSIONS
|
Two more terms from Ryan Propper, Dec 10 2008
a(14) from Paul Bourdelais, Mar 03 2021
|
|
|
STATUS
|
approved
|
| |
|
|
