a(n) is the number of central ideals of a garland of order 2n, i.e., a(n) = g(2n,n), where g(n,k) is the number of ideals of size k in a garland (or double fence) of order n (see A137278).

A136029

a(n) is the number of central ideals of a garland of order 2n, i.e., a(n) = g(2n,n), where g(n,k) is the number of ideals of size k in a garland (or double fence) of order n (see A137278).