Number of strings over Z_4 of length n with trace 1 and subtrace 2.

Terms

a(0) =0a(1) =2a(2) =6a(3) =16a(4) =56a(5) =192a(6) =896a(7) =4096a(8) =17280a(9) =69632a(10) =270336a(11) =1048576a(12) =4130816a(13) =16515072a(14) =66584576a(15) =268435456a(16) =1077903360a(17) =4311744512a(18) =17213423616a(19) =68719476736a(20) =274609995776