a(n) = 11*3^n.

Terms

a(0) =11a(1) =33a(2) =99a(3) =297a(4) =891a(5) =2673a(6) =8019a(7) =24057a(8) =72171a(9) =216513a(10) =649539a(11) =1948617a(12) =5845851a(13) =17537553a(14) =52612659a(15) =157837977a(16) =473513931a(17) =1420541793a(18) =4261625379a(19) =12784876137a(20) =38354628411a(21) =115063885233a(22) =345191655699