a(n) is the number of ways to insert single pairs of parenthesis to completely separate n identical objects in a straight line such that at least one of the objects at the two ends is not enclosed.
A157418
a(n) is the number of ways to insert single pairs of parenthesis to completely separate n identical objects in a straight line such that at least one of the objects at the two ends is not enclosed.
Terms
- a(0) =1a(1) =2a(2) =5a(3) =16a(4) =55a(5) =202a(6) =773a(7) =3052a(8) =12339a(9) =50830a(10) =212593a(11) =900368a(12) =3853551a(13) =16641554a(14) =72423661a(15) =317312532a(16) =1398490091a(17) =6195882006a(18) =27578607593a(19) =123270393880a(20) =553075982311
External references
- oeis: A157418