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
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
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