OFFSET
1,3
COMMENTS
a(n) is odd for n > 0. Next term > 17200. - Julián Aguirre, Apr 22 2011
a(16) > 2*10^5. - Robert Price, Mar 14 2015
EXAMPLE
a(3)=13 and 1 + 2*5^13 = 2441406251 is prime.
MATHEMATICA
Select[Range[0, 16000], PrimeQ[2*5^#+1]&] (* Julián Aguirre, Apr 22 2011 *)
PROG
(Sage)
[n for n in range(1500) if is_prime(2*5^n+1)]
# Julián Aguirre, Apr 22 2011
(PARI) is(n)=ispseudoprime(2*5^n+1) \\ Charles R Greathouse IV, Jun 12 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Labos Elemer, Jan 12 2001
EXTENSIONS
Edited by Joerg Arndt, Apr 22 2011
Terms 1443,...,12357 from Julián Aguirre, Apr 22 2011
a(14)-a(15) from Robert Price, Mar 14 2015
STATUS
approved