Number of symmetric foldings of a strip of n blank stamps.

Terms

a(0) =1a(1) =2a(2) =2a(3) =4a(4) =6a(5) =8a(6) =18a(7) =20a(8) =56a(9) =48a(10) =178a(11) =132a(12) =574a(13) =348a(14) =1870a(15) =1008a(16) =6144a(17) =2812a(18) =20314a(19) =8420a(20) =67534a(21) =24396a(22) =225472a(23) =74756a(24) =755672a(25) =222556a(26) =2540406a(27) =693692a(28) =8564622a(29) =2107748