G.f.: 1/(1-6*x+8*x^3).

Terms

a(0) =1a(1) =6a(2) =36a(3) =208a(4) =1200a(5) =6912a(6) =39808a(7) =229248a(8) =1320192a(9) =7602688a(10) =43782144a(11) =252131328a(12) =1451966464a(13) =8361541632a(14) =48152199168a(15) =277297463296