Somebody marked the six faces of a die with the numbers 1, 2 and 3 - each number twice. The die was put on a table. Four people - Abu, Babu, Calu and Dabu - sat around the table so that each one was able to see only three sides of the die at a glance.
* Abu sees the number 1 and two even numbers.
* Babu and Calu can see three different numbers each.
* Dabu sees number 2 twice and he can't remember the third number. What number is face down on the table?