a(n) = 2*n*3^(n-1).

Terms

a(0) =2a(1) =12a(2) =54a(3) =216a(4) =810a(5) =2916a(6) =10206a(7) =34992a(8) =118098a(9) =393660a(10) =1299078a(11) =4251528a(12) =13817466a(13) =44641044a(14) =143489070a(15) =459165024a(16) =1463588514a(17) =4649045868a(18) =14721978582a(19) =46490458680a(20) =146444944842a(21) =460255540932