a(n) = Sum_{k=0..floor(n/2)} binomial(n-k, k-1)*2^(n-k-1)*(3/2)^(k-1).

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =10a(5) =26a(6) =91a(7) =260a(8) =820a(9) =2420a(10) =7381a(11) =22022a(12) =66430a(13) =198926a(14) =597871a(15) =1792520a(16) =5380840a(17) =16139240a(18) =48427561a(19) =145272842a(20) =435848050a(21) =1307514626a(22) =3922632451a(23) =11767808780a(24) =35303692060a(25) =105910810460a(26) =317733228541a(27) =953198888462