148099380domain: NAppears in sequencesNumber of perfect matchings on an n X n L-shaped graph.at n=20A079472Constant term in the reduction by (x^2 -> x+1) of the polynomial p(n,x) given in Comments.at n=21A192872Denominators a(n) of Pythagorean approximations b(n)/a(n) to 1/2.at n=19A195547