OFFSET
1,2
COMMENTS
Note that a(n) mod 27 = a(n) mod 9 = a(n) mod 3 = 1.
The Maple program yields the first seven terms; easily adjustable for obtaining more terms. However, a(4) has 44 digits, a(5) has 140 digits, a(6) has 432 digits and a(7) has 1308 digits. - Emeric Deutsch, Nov 22 2009
LINKS
Eric Weisstein's World of Mathematics, Central Binomial Coefficient.
Eric Weisstein's World of Mathematics, Binomial Sums.
MAPLE
a := proc (n) options operator, arrow: (sum(binomial(2*k, k), k = 0 .. 3^n-1))/3^(2*n) end proc: seq(a(n), n = 1 .. 7); # Emeric Deutsch, Nov 22 2009
MATHEMATICA
Table[(1/3^n)^2 * Sum[Binomial[2 k, k], {k, 0, 3^n - 1}], {n, 1, 5}] (* G. C. Greubel, Jul 01 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alexander Adamchuk, Nov 15 2009
EXTENSIONS
a(4) from Emeric Deutsch, Nov 22 2009
STATUS
approved