Help with multiplication

Cell A1 = 3
Cell A2 = 4

Is there a formula to calculate
(3*4)+(2*4)+(1*4)

I need to multiply every integer less than the number in cell A1 and greater than zero by the number cell in A2. I was thinking factorial, but that's not it... Can't remember from my math days.

Thanks for your help!

=a2 * a1 * (1 + a1) / 2

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