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

Terms

a(0) =-1a(1) =1a(2) =3a(3) =11a(4) =31a(5) =87a(6) =239a(7) =655a(8) =1791a(9) =4895a(10) =13375a(11) =36543a(12) =99839a(13) =272767a(14) =745215a(15) =2035967a(16) =5562367a(17) =15196671a(18) =41518079a(19) =113429503a(20) =309895167a(21) =846649343a(22) =2313089023a(23) =6319476735a(24) =17265131519a(25) =47169216511a(26) =128868696063a(27) =352075825151a(28) =961889042431