The number of semi-meanders with n top arches and concentric arches within the starting arch or a starting arch with length one.

A330269

The number of semi-meanders with n top arches and concentric arches within the starting arch or a starting arch with length one.

Terms

    a(0) =1a(1) =1a(2) =2a(3) =4a(4) =8a(5) =18a(6) =42a(7) =108a(8) =282a(9) =786a(10) =2192a(11) =6402a(12) =18600a(13) =55978a(14) =167256a(15) =514102a(16) =1567976a(17) =4896164a(18) =15170630a(19) =47957260a(20) =150468678a(21) =480371736a(22) =1522649458a(23) =4900568718a(24) =15665593150a(25) =50761432998a(26) =163431901126a(27) =532624603680

External references