a(n) = -3*a(n-1) + a(n-3), with a(0)=0, a(1)=-3, a(2)=12.

Terms

a(0) =0a(1) =-3a(2) =12a(3) =-36a(4) =105a(5) =-303a(6) =873a(7) =-2514a(8) =7239a(9) =-20844a(10) =60018a(11) =-172815a(12) =497601a(13) =-1432785a(14) =4125540a(15) =-11879019a(16) =34204272a(17) =-98487276a(18) =283582809a(19) =-816544155a(20) =2351145189a(21) =-6769852758a(22) =19493014119a(23) =-56127897168a(24) =161613838746a(25) =-465348502119