设 a = n - 2006
则 2007 - n = -a + 1
a^2 - a + 1 = 1
a^2 - a = 0
a = 0 or a = 1
若a = 0
n - 2006 = 0
原式 = 0
若a = 1
2007 - n = 0
原式 = 0