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)=2.

Terms

a(0) =1a(1) =1a(2) =2a(3) =2a(4) =2a(5) =2a(6) =6a(7) =10a(8) =14a(9) =26a(10) =50a(11) =90a(12) =162a(13) =290a(14) =582a(15) =1090a(16) =2006a(17) =3794a(18) =7458a(19) =14306a(20) =27074a(21) =51762a(22) =103062a(23) =200410a(24) =385070a(25) =747274a(26) =1492050a(27) =2929754a(28) =5702258a(29) =11151778