a(n) = 4 - 15 * 2^n + 12 * 3^n.

Terms

a(0) =1a(1) =10a(2) =52a(3) =208a(4) =736a(5) =2440a(6) =7792a(7) =24328a(8) =74896a(9) =228520a(10) =693232a(11) =2095048a(12) =6315856a(13) =19009000a(14) =57149872a(15) =171695368a(16) =515577616a(17) =1547715880a(18) =4645113712a(19) =13939273288a(20) =41825684176a(21) =125492781160a(22) =376509800752