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%I #5 Nov 07 2016 12:06:05
%S 1,3,43263,6568517413771094628,
%T 748787983804424579516665098357127267955239740580277791815018327
%N Least number in A001764 divisible by 3^n: a(n) = A001764(3^n-1).
%C Only numbers in A001764 not divisible by 3 are: A001764((3^n-1)/2) for n>=0.
%F a(n) = C(3^(n+1)-3, 3^n-1) / (2*3^n-1).
%t Table[Binomial[3^(n + 1) - 3, 3^n - 1]/(2*3^n - 1), {n,0,10}] (* _G. C. Greubel_, Nov 07 2016 *)
%o (PARI) a(n)=binomial(3^(n+1)-3,3^n-1)/(2*3^n-1)
%Y Cf. A001764; A135759.
%K nonn
%O 0,2
%A _Paul D. Hanna_, Dec 02 2007