a(n) = 2*a(n-1)+3*a(n-2)-6*a(n-3) starting a(0)=a(1)=0, a(2)=1.

Terms

a(0) =0a(1) =0a(2) =1a(3) =2a(4) =7a(5) =14a(6) =37a(7) =74a(8) =175a(9) =350a(10) =781a(11) =1562a(12) =3367a(13) =6734a(14) =14197a(15) =28394a(16) =58975a(17) =117950a(18) =242461a(19) =484922a(20) =989527a(21) =1979054a(22) =4017157a(23) =8034314a(24) =16245775a(25) =32491550a(26) =65514541a(27) =131029082a(28) =263652487a(29) =527304974