Number of -1..1 arrays x(0..n-1) of n elements with zero sum and no two neighbors equal.

Terms

a(0) =1a(1) =2a(2) =6a(3) =8a(4) =14a(5) =32a(6) =56a(7) =100a(8) =204a(9) =388a(10) =722a(11) =1416a(12) =2750a(13) =5256a(14) =10222a(15) =19944a(16) =38650a(17) =75272a(18) =147142a(19) =287120a(20) =561018a(21) =1098752a(22) =2152092a(23) =4217620a(24) =8276376a(25) =16250292a(26) =31921374a(27) =62754072a(28) =123440514a(29) =242921784