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

Terms

a(0) =1a(1) =2a(2) =1a(3) =5a(4) =-2a(5) =17a(6) =-23a(7) =74a(8) =-143a(9) =365a(10) =-794a(11) =1889a(12) =-4271a(13) =9938a(14) =-22751a(15) =52565a(16) =-120818a(17) =278513a(18) =-640967a(19) =1476506a(20) =-3399407a(21) =7828925a(22) =-18027146a(23) =41513921a(24) =-95595359a(25) =220137122a(26) =-506923199a(27) =1167334565