5 sigma n=1 n (n+1) (n+2) / 3

1(1+1)(1+2)/3=2
2(2+1)(2+2)/3=8
3(3+1)(3+2)/3=20
4(4+1)(4+2)/3=40
5(5+1)(5+2)/3=70

2+8+20+40+70=140

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