It is an application of a simplemultiplication.
Digit is incremented each time it is clear, it becomes more andmore difficult.

I think what will change each time you challenge an issue thatwas clear, and play any number of times.
Since it can be used to save time that was clear, it also allowsyou to compete with friends.

Difficult to calculate from a simple calculation, adults canenjoy from children.
Because it is a stanza in the 10 questions, the problem will beable to play in the gap time.I think it's also ideal for trainingthe brain.

How many digits can you calculate?