a(n) = 9 - 28 * 2^n + 20 * 3^n.

Terms

a(0) =1a(1) =13a(2) =77a(3) =325a(4) =1181a(5) =3973a(6) =12797a(7) =40165a(8) =124061a(9) =379333a(10) =1152317a(11) =3485605a(12) =10514141a(13) =31657093a(14) =95200637a(15) =286060645a(16) =859099421a(17) =2579133253a(18) =7741069757a(19) =23230549285a(20) =69706327901a(21) =209148343813a(22) =627503751677