1x2 + 2x3 + 3x4 + ······ + 101x101 = what

1x2 + 2x3 + 3x4 + ······ + 101x101 = what

It should be: "1x2 + 2x3 + 3x4 + ······ + 100x101", right? Dim I as long, Isum as long Isum = 0 for I = 1 to 100 Isum = Isum + I * (I + 1) next I Debug.Print Isum running result: Isum = 343400

3x (1x2+2X3+3x4...+99x100)=

99x100x101

11x2+12x3+13x4+14x5+… +199x100．

11x2+12x3+13x4+14x5+… +199x100，=（1-12）+（12-13）+（13-14）+（14-15）+… +（199-1100），=1-12+12-13+13-14+14-15+… +199-1100，=1-1100，=99100．

1x2+2x3+3x4+.99x100=?

1x2+2x3+3x4+… +n(n+1)
=1x(1+1)+2x(2+1)+3x(3+1)+… n(n+1)
=(1^2+2^2+3^2+… +n^2)+(1+2+3+… +n)
=n(n+1)(2n+1)/6+n(n+1)/2
=n(n+1)[(2n+1)+3]/6
You can make n = 99 and bring it in