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%I #9 Mar 07 2017 00:13:58
%S 1,1,-1,1,1,-1,-1,-1,-1,1,1,-1,1,1,-1,1,1,1,-1,-1,1,-1,-1,1,1,1,-1,1,
%T 1,-1,1,1,-1,-1,-1,-1,1,1,-1,1,1,-1,-1,-1,1,1,1,-1,1,1,-1,-1,-1,1,-1,
%U -1,1,-1,-1,1,1,1,1,-1,-1,1,-1,-1,1,-1,-1
%N a(n) = (-1)^A186038(n).
%C Hankel transform is A186040.
%H G. C. Greubel, <a href="/A186039/b186039.txt">Table of n, a(n) for n = 0..1000</a>
%F a(n) = (-1)^log_3(A002426(n)/numerator(A002426(n)/3^n)).
%t Join[{1}, Table[(-1)^(Log[3, GegenbauerC[n, -n, -1/2]/ (Numerator[ GegenbauerC[n, -n, -1/2]/3^n])]), {n,1,50}]] (* _G. C. Greubel_, Mar 06 2017 *)
%Y Cf. A002426, A186038, A186040.
%K sign,easy
%O 0
%A _Paul Barry_, Feb 11 2011