a(0)=1, a(1)=4, a(n)=9*a(n-1)-16*a(n-2) for n>1.

Terms

a(0) =1a(1) =4a(2) =20a(3) =116a(4) =724a(5) =4660a(6) =30356a(7) =198644a(8) =1302100a(9) =8540596a(10) =56031764a(11) =367636340a(12) =2412218836a(13) =15827788084a(14) =103854591380a(15) =681446713076