a(a+1)(a+2)(a+3)+1 = (a^2+3a+1)(a^2+3a+1)
√[a(a+1)(a+2)(a+3)+1] - (a+1)^2 =a^2+3a+1-(a^2+2a+1) = a;
2001*2002*2003*2004+1=(2002*2003)*(2001*2004)+1
=(2002*2003-1)*(2002*2003-1)
√(2001*2002*2003*2004+1) - 2002^2=2002*2003-1 - 2002^2= 2001
题目到底是连加还是连乘啊?