a(n) is the number of arches with a length of one and exactly one covering arch for semi-meanders with n top arches.

A346757

a(n) is the number of arches with a length of one and exactly one covering arch for semi-meanders with n top arches.

Terms

    a(0) =0a(1) =2a(2) =2a(3) =12a(4) =20a(5) =88a(6) =180a(7) =716a(8) =1648a(9) =6244a(10) =15512a(11) =57188a(12) =149892a(13) =543324a(14) =1481636a(15) =5310764a(16) =4930380a(17) =53102508a(18) =152935148a(19) =540918660a(20) =1588618212a(21) =5595773136a(22) =16701973552

External references