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