G.f.: (1-2*x-5*x^2+4*x^3)/((1-4*x)*(1-x)^2).

Terms

a(0) =1a(1) =4a(2) =10a(3) =32a(4) =118a(5) =460a(6) =1826a(7) =7288a(8) =29134a(9) =116516a(10) =466042a(11) =1864144a(12) =7456550a(13) =29826172a(14) =119304658a(15) =477218600a(16) =1908874366a(17) =7635497428a(18) =30541989674a(19) =122167958656a(20) =488671834582