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

Terms

a(0) =3a(1) =7a(2) =23a(3) =67a(4) =203a(5) =607a(6) =1823a(7) =5467a(8) =16403a(9) =49207a(10) =147623a(11) =442867a(12) =1328603a(13) =3985807a(14) =11957423a(15) =35872267a(16) =107616803a(17) =322850407a(18) =968551223a(19) =2905653667a(20) =8716961003a(21) =26150883007a(22) =78452649023a(23) =235357947067a(24) =706073841203