a(n)=Sum{T(2i,n-2i): i=0,1,...,[ n/2 ]}, array T as in A049600.

Terms

a(0) =0a(1) =0a(2) =2a(3) =3a(4) =12a(5) =25a(6) =76a(7) =182a(8) =504a(9) =1275a(10) =3410a(11) =8811a(12) =23256a(13) =60580a(14) =159094a(15) =415715a(16) =1089648a(17) =2850645a(18) =7466468a(19) =19541994a(20) =51170460a(21) =133951675a(22) =350713222a(23) =918141623a(24) =2403786672a(25) =6293097000a(26) =16475700746a(27) =43133687427a(28) =112925875764