Number of strings over Z_4 of length n with trace 0 and subtrace 0.

Terms

a(0) =1a(1) =2a(2) =4a(3) =8a(4) =56a(5) =272a(6) =1184a(7) =4736a(8) =17536a(9) =65792a(10) =254464a(11) =1015808a(12) =4130816a(13) =16781312a(14) =67641344a(15) =270565376a(16) =1077968896a(17) =4295032832a(18) =17146445824a(19) =68585259008a(20) =274609995776