968561domain: NAppears in sequencesa(n) = a(n-1) + 20*a(n-2), n >= 2; a(0)=1, a(1)=1.at n=9A053428a(n) = (n^(2n) - (n-1)^(2n))/(2n-1).at n=4A280305Number of lattice paths from (0,0) to (n,n) using Euclid's orchard as a step-set.at n=13A308087