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