Only for positives:
(x+a)(x+b)(x+c) = x^3 + (a+b+c)x^2 + ((a*b)+(a*c)+(b*c))x + ABC.
Eg, (x+1)(x+3)(x+3) = x^3 + (1+3+3)x^2 + ((1*3)+(1*3)+(3*3))x + (1*3*3) = x^3 + 7x^2 + 15x + 9.
Probably some flaws in this, I only got this when my maths teacher made us do over 25 of them. Seemed to work for me though. If someone's bothered, try and figure out how to make this work for negatives, or when the coefficient of x is more than one.