Number of non-palindromic n-tuples of 4 distinct elements.

Terms

a(0) =0a(1) =12a(2) =48a(3) =240a(4) =960a(5) =4032a(6) =16128a(7) =65280a(8) =261120a(9) =1047552a(10) =4190208a(11) =16773120a(12) =67092480a(13) =268419072a(14) =1073676288a(15) =4294901760a(16) =17179607040a(17) =68719214592a(18) =274876858368