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%I #2 Mar 30 2012 18:50:59
%S 1,2,4,20,56,336,1056,6864,22880,155584,537472,3762304,13312768,
%T 95091200,342328320,2481880320,9051563520,66378132480
%N a(n) = x(n) * 2^((n mod 2 - 1)/2), with x(n)=Sum(x(k)*x(n-k-1):0<=k<n), x(0)=SQRT(2).
%e x(1) = 2;
%e x(2) = 5.6568... = a(2)*SQRT(2);
%e x(3) = 20;
%e x(4) = 79.1959... = a(4)*SQRT(2);
%e x(5) = 336;
%e x(6) = 1493.4095... = a(6)*SQRT(2).
%Y Cf. A000108.
%K nonn
%O 0,2
%A _Reinhard Zumkeller_, Feb 06 2008
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