√(n² + 1) = [n;2n]

√d = n + (√d - n) mit d = n² + 1

a0 = n

    1          1      (√d + n)   (√d + n)   2n + (√d - n)        (√d - n)
-------- = -------- × -------- = -------- = ------------- = 2n + --------
(√d - n)   (√d - n)   (√d + n)       1            1                  1

a1 = 2n