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a(n) = Sum_{i=1..floor((n+1)/4)} a(2*i-1) * a(n-2*i+1), with a(1)=a(3)=2 and a(2)=1.
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%I #6 Jul 21 2019 18:06:17

%S 2,1,2,4,8,16,40,96,224,528,1376,3520,8864,22272,59648,156992,407808,

%T 1060864,2872960,7701504,20460032,54299904,148601856,402977792,

%U 1084414464,2918055936,8035600384,21980652544,59769698304,162381037568,449715144704

%N a(n) = Sum_{i=1..floor((n+1)/4)} a(2*i-1) * a(n-2*i+1), with a(1)=a(3)=2 and a(2)=1.

%K nonn

%O 1,1

%A _Clark Kimberling_

%E a(26) corrected by _Sean A. Irvine_, Jul 21 2019