a(n) = 3*a(n-2) - a(n-3), with a(0)=0, a(1)=a(2)=-3.

Terms

a(0) =0a(1) =-3a(2) =-3a(3) =-9a(4) =-6a(5) =-24a(6) =-9a(7) =-66a(8) =-3a(9) =-189a(10) =57a(11) =-564a(12) =360a(13) =-1749a(14) =1644a(15) =-5607a(16) =6681a(17) =-18465a(18) =25650a(19) =-62076a(20) =95415a(21) =-211878a(22) =348321a(23) =-731049a(24) =1256841a(25) =-2541468a(26) =4501572a(27) =-8881245a(28) =16046184a(29) =-31145307