Number of non-palindromic n-tuples of 3 distinct elements.

Terms

a(0) =0a(1) =6a(2) =18a(3) =72a(4) =216a(5) =702a(6) =2106a(7) =6480a(8) =19440a(9) =58806a(10) =176418a(11) =530712a(12) =1592136a(13) =4780782a(14) =14342346a(15) =43040160a(16) =129120480a(17) =387400806a(18) =1162202418a(19) =3486725352a(20) =10460176056a(21) =31380882462a(22) =94142647386a(23) =282429005040a(24) =847287015120