8135830269domain: NAppears in sequencesa(n) = 7*3^n.at n=19A005032Number of ternary trees (A001764) with n nodes and maximal diameter.at n=19A064017a(n) = (7*3^n - 4*0^n)/3.at n=20A082541Expansion of (1-3*x+12*x^2)/((1-3*x)*(1+3*x)).at n=20A091103a(n) = 3*a(n-1) for n>2; a(0)=1, a(1)=3, a(2)=7.at n=21A141495