OFFSET
0,1
COMMENTS
Next two terms have 15635 and 1024610093 digits respectively. [Corrected by Michael S. Branicky and Sean A. Irvine, Nov 12 2022]
LINKS
C. K. Caldwell, Pepin's Test.
FORMULA
a(n) = 3^((F(n)-1)/2) where F(n) is a Fermat number (A000215).
EXAMPLE
a(1) = 3^((F(1)-1)/2) = 3^((5-1)/2) = 3^2 = 9.
MATHEMATICA
A000215[n_]:=2^(2^n)+1; a[n_]:=3^((A000215[n]-1)/2); Array[a, 4, 0] (* Stefano Spezia, Sep 14 2024 *)
PROG
(Python)
def a(n): return 3**(2**(2**n-1))
print([a(n) for n in range(4)]) # Michael S. Branicky, Nov 12 2022
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason Earls, Apr 02 2001
EXTENSIONS
Corrected offset, formula and example Harry J. Smith, Jul 04 2009
STATUS
approved