19181424995domain: NAppears in sequencesa(n) = 2*a(n-1) + a(n-2) - a(n-3) for n >= 3, starting with a(0) = 1, a(1) = 3, and a(2) = 6.at n=29A006356Top line of 3-wave sequence A038196, also bisection of A006356.at n=15A038213Expansion of (1-x)/(1-2*x-x^2+x^3).at n=30A077998Expansion of x + 1/(-x - 1/(-x - 1/(-x + 1))).at n=29A373567