168780domain: NAppears in sequences2n^4+6n^2+4 = 2(n^2+1)(n^2+2).at n=16A120571Irregular triangle read by rows: T(n, k) is the number of 2n-step closed walks on the square lattice having algebraic area k; n >= 0, 0 <= k <= floor(n^2/4).at n=20A352838E.g.f. A(x) satisfies: A(x) = 1 + x * A(-2 * log(1-x)).at n=5A355126