G.f.: (1+2x)(1+2x+4x^2)/(1-3x-8x^3-8x^4).

Terms

a(0) =1a(1) =7a(2) =29a(3) =103a(4) =373a(5) =1407a(6) =5277a(7) =19639a(8) =73157a(9) =272943a(10) =1018157a(11) =3796839a(12) =14159317a(13) =52806751a(14) =196940221a(15) =734469911a(16) =2739138277a(17) =10215390607a(18) =38097452877a(19) =142081224135a(20) =529879903477