a(n) = 7*a(n-1) - 6*a(n-2), n>1; a(0)=1, a(1)=3.

Terms

a(0) =1a(1) =3a(2) =15a(3) =87a(4) =519a(5) =3111a(6) =18663a(7) =111975a(8) =671847a(9) =4031079a(10) =24186471a(11) =145118823a(12) =870712935a(13) =5224277607a(14) =31345665639a(15) =188073993831