a(1)=0, a(2)=1; thereafter a(n) = A238823(n-1)-2*a(n-1)-a(n-2).

Terms

a(0) =0a(1) =1a(2) =1a(3) =3a(4) =7a(5) =17a(6) =43a(7) =105a(8) =262a(9) =643a(10) =1590a(11) =3911a(12) =9643a(13) =23743a(14) =58502a(15) =144099a(16) =355009a(17) =874545a(18) =2154505a(19) =5307663a(20) =13075683a(21) =32212375a(22) =79356454a(23) =195497421a(24) =481615082a(25) =1186475969a(26) =2922926441a(27) =7200734309a(28) =17739268544a(29) =43701326725