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A137697 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). 1

%I

%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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Last modified October 15 11:03 EDT 2018. Contains 316224 sequences. (Running on oeis4.)