Σxy=ΣΣx(m-x)
Σm^2(m-1)/2-(m-1)m(2m-1)/6
Σ3m^3-3m^2-2m^3+3m^2-m/6
Σ(m^3-m)/6
(n^4+2n^3+n^2-2n(n+1))/24
(n^4+2n^3-n^2-2n)/24
3Σxy/Σ(m-1)
<xy+yz+zx>=(n^4+2n^3-n^2-2n)/4(n-2)(n-1)
(n^2+3n+2)n/4(n-2)
<xyz>
<x(m-x)(n-m)>/m(m-1)/2
<(n-m)(mx-x^2)>/((n-1)(n-2))/2)
(n-m)(m^3-m)/6
n(m^3-m)/6-(m^4-m^2)/6,m=2->n-1
{15n((n-1)^3+2(n-1)^2-(n-1)-2)-2(6(n-1)^4+15(n-1)^3+10(n-1)^2-1)
+10(2(n-1)^2+3(n-1)+1)}/180(n-2)