a(n) = 2*a(n-1) + 4*a(n-2), a(0)=1, a(1)=1.

Terms

a(0) =1a(1) =1a(2) =6a(3) =16a(4) =56a(5) =176a(6) =576a(7) =1856a(8) =6016a(9) =19456a(10) =62976a(11) =203776a(12) =659456a(13) =2134016a(14) =6905856a(15) =22347776a(16) =72318976a(17) =234029056a(18) =757334016a(19) =2450784256a(20) =7930904576a(21) =25664946176a(22) =83053510656a(23) =268766806016a(24) =869747654656