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a(n) = Sum_{i=1..floor((n+2)/4)} a(2i-1)*a(n-2i+1), with a(1)=3 and a(2)=a(3)=1.
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%I #7 Jul 31 2019 03:03:27

%S 3,1,1,3,9,28,87,270,838,2682,8568,27325,87087,284940,929773,3026424,

%T 9843471,32691629,108290562,357839667,1181136576,3967571310,

%U 13290977466,44410377199,148240940865,501864577470,1694984858142,5711630686332

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

%K nonn

%O 1,1

%A _Clark Kimberling_

%E Offset corrected and title improved by _Sean A. Irvine_, Jul 30 2019