Problem #366
Prime Dices
You have a set of dice, where each die has a number of sides that corresponds to a prime number less than 10^7. For example, the set includes dice with 2, 3, 5, 7, and other prime numbers of sides.
A die is chosen randomly from this set. After selecting the die, you keep tossing it until every face of the die has appeared at least once. For instance, for a 3-sided die, you might toss the die multiple times until you have seen all three faces (1, 2, and 3) at least once.
The sequence of tosses could look something like 2, 1, 1, 2, 3, which means it took 5 tosses to see all three faces.
Your task is to find the expected number of tosses required to see all faces of the die you picked. Report the result modulo 10^9 + 7.