x[1] = 1, x[2] = 3
x[n+2] = (4n+2)x[n+1] + x[n]
y[1] = 1, y[2] = 1
y[n+2] = (4n+2)y[n+1] + y[n]

この数列においてx[n]/y[n]がeに収束することの証明