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A160567 a(n)=4*(a(n-1)a(n-3)-a(n-2)^2)/a(n-4), a(1)=a(2)=a(3)=1, a(4)=-4.

%I A160567 #4 Feb 25 2015 14:26:00
%S A160567 1,1,1,-4,-20,-144,704,34816,1101824,12124160,-4499439616,
%T A160567 -586464362496,-99309307559936,33947352788107264,26466630265219317760,
%U A160567 25787111566764821970944,-7045529183328701486465024
%N A160567 a(n)=4*(a(n-1)a(n-3)-a(n-2)^2)/a(n-4), a(1)=a(2)=a(3)=1, a(4)=-4.
%C A160567 a(n+1) is the Hankel transform of A160565.
%p A160567 A160567 := proc(n)
%p A160567     option remember;
%p A160567     if n < 5 then
%p A160567         op(n,[1,1,1,-4]);
%p A160567     else
%p A160567         4*(procname(n-1)*procname(n-3)-procname(n-2)^2)/procname(n-4) ;
%p A160567     end if;
%p A160567 end proc: # _R. J. Mathar_, Feb 25 2015
%Y A160567 Cf. A050512.
%K A160567 easy,sign
%O A160567 0,4
%A A160567 _Paul Barry_, May 19 2009