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

Terms

a(0) =0a(1) =0a(2) =0a(3) =4a(4) =-4a(5) =0a(6) =8a(7) =-16a(8) =12a(9) =20a(10) =-80a(11) =116a(12) =-4a(13) =-376a(14) =884a(15) =-764a(16) =-1308a(17) =5816a(18) =-9128a(19) =648a(20) =32008a(21) =-79608a(22) =73100a(23) =122020a(24) =-574044a(25) =937456a(26) =-97748a(27) =-3366892a(28) =8659492a(29) =-8276056