√(2005×2006×2007×2008+1)
=√(2005×2008×2006×2007+1)
=√[2005×(2005+3)×(2005+1)×(2005+2)+1]
=√[(2005²+3×2005)×(2005²+3×2005+2)+1]
=√[(2005²+3×2005)²+2×(2005²+3×2005)+1]
=√[(2005²+3×2005+1)]²
=2005²+3×2005+1
=(2005+1)²+2005
=2006²+2005
=4026041