n(n-1)(n+1)(n+2)+1 =(n^2-n)(n^2+3n+2)+1 =n^4+3n^3+2n^2-n^3-3n^2-2n+1 =n^4+2n^3-n^2-2n+1 =n^4+2n^3+n^2-(2n^2+2n-1) =n^2(n+1)^2-2n(n+1)+1 =(n^2+n-1)^2 既然可以化成,就是相等的
n(n-1)(n+1)(n+2)+1等不等于(n^n+n-1)^2
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