a(n) is the number of semi-meanders with n top arches that have both an arch of length 1 adjacent to the center of the top arch configuration and an arch of length 1 starting or ending the top arch configuration.
A337581
a(n) is the number of semi-meanders with n top arches that have both an arch of length 1 adjacent to the center of the top arch configuration and an arch of length 1 starting or ending the top arch configuration.
Terms
- a(0) =1a(1) =2a(2) =4a(3) =8a(4) =16a(5) =40a(6) =96a(7) =264a(8) =696a(9) =2016a(10) =5624a(11) =16840a(12) =48792a(13) =149512a(14) =445112a(15) =1387384a(16) =4215496a(17) =13312752a(18) =41097864a(19) =131146520a(20) =410045672a(21) =1319612232a(22) =4169110888a(23) =13511677040a(24) =43060097728a(25) =140383359392
External references
- oeis: A337581