Don Colton's Risk Dice Roller

(Risk is a trademark of Parker Bros / Hasbro for their board game.)
Wikipedia Article, Attacking

How many attacking armies
How many defending armies
How many skirmishes (max)

Skirmish 1   2 4 3   5 2 attacker loses X, defender loses X
Skirmish 2   2 1 6   2 3 attacker loses X, defender loses X
Skirmish 3   3 6 5   2 5 attacker loses X, defender loses X
Skirmish 4   6 3 3   6 6 attacker loses X, defender loses X