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%I #6 Jul 21 2019 13:27:14
%S 1,1,3,3,3,3,12,21,30,66,138,264,525,1029,2271,4620,9291,19335,41430,
%T 86556,178689,373854,814269,1726698,3620550,7688712,16786875,35952933,
%U 76375821,163325109,358773663,773646114,1656489261,3572265090,7856043150,17039803998
%N a(n) = Sum_{i=1..floor((n+1)/4)} a(2*i-1) * a(n-2*i+1), with a(1)=a(2)=1 and a(3)=3.
%K nonn
%O 1,3
%A _Clark Kimberling_
%E a(28) corrected by _Sean A. Irvine_, Jul 20 2019