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%I #18 Apr 03 2023 10:36:10
%S 3,9,6561,
%T 11790184577738583171520872861412518665678211592275841109096961
%N Pepin's test numbers.
%C Next two terms have 15635 and 1024610093 digits respectively. [Corrected by _Michael S. Branicky_ and _Sean A. Irvine_, Nov 12 2022]
%H C. K. Caldwell, <a href="https://t5k.org/glossary/page.php?sort=PepinsTest">Pepin's Test</a>
%F a(n) = 3^((F(n)-1)/2) where F(n) is a Fermat number (A000215).
%e a(1) = 3^((F(1)-1)/2) = 3^((5-1)/2) = 3^2 = 9.
%o (Python)
%o def a(n): return 3**(2**(2**n-1))
%o print([a(n) for n in range(4)]) # _Michael S. Branicky_, Nov 12 2022
%K nonn
%O 0,1
%A _Jason Earls_, Apr 02 2001
%E Corrected offset, formula and example _Harry J. Smith_, Jul 04 2009
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