Number of 2n-bead balanced binary strings, rotationally equivalent to reversed complement.

Terms

a(0) =1a(1) =2a(2) =6a(3) =20a(4) =54a(5) =152a(6) =348a(7) =884a(8) =1974a(9) =4556a(10) =10056a(11) =22508a(12) =48636a(13) =106472a(14) =228444a(15) =491120a(16) =1046454a(17) =2228192a(18) =4713252a(19) =9961436a(20) =20960904a(21) =44038280a(22) =92252100a(23) =192937940a(24) =402599676a(25) =838860152a(26) =1744723896a(27) =3623869388a(28) =7515962172