a(n) is the number of induced subgraphs with odd number of edges in the cycle graph C(n).

Terms

a(0) =0a(1) =4a(2) =4a(3) =16a(4) =24a(5) =64a(6) =112a(7) =256a(8) =480a(9) =1024a(10) =1984a(11) =4096a(12) =8064a(13) =16384a(14) =32512a(15) =65536a(16) =130560a(17) =262144a(18) =523264a(19) =1048576a(20) =2095104a(21) =4194304a(22) =8384512a(23) =16777216a(24) =33546240a(25) =67108864a(26) =134201344a(27) =268435456a(28) =536838144a(29) =1073741824