OFFSET
0,3
COMMENTS
The number of digits for the terms begin:
[1, 1, 2, 9, 31, 97, 298, 902, 2715, 8155, 24478, 73446, 220354, ...].
FORMULA
a(n) = A001764( (3^n-1)/2 ) = binomial( 3*(3^n-1)/2, (3^n-1)/2 ) / 3^n.
a(n) == 1 (mod 3).
EXAMPLE
PROG
(PARI) a(n)=binomial(3*(3^n-1)/2, (3^n-1)/2)/3^n
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Dec 05 2011
STATUS
approved