a(n) = 2*a(n-1) + 6*a(n-2).

Terms

a(0) =1a(1) =1a(2) =8a(3) =22a(4) =92a(5) =316a(6) =1184a(7) =4264a(8) =15632a(9) =56848a(10) =207488a(11) =756064a(12) =2757056a(13) =10050496a(14) =36643328a(15) =133589632a(16) =487039232a(17) =1775616256a(18) =6473467904a(19) =23600633344a(20) =86042074112a(21) =313687948288