21, 45, 78, 3, 6, 9 are all multiples of 3 and can be made with just 9 numbers (No need of 0).
1) 6, 9, 12, 30, 45, 78
2) 3, 6, 9, 24, 78, 105
I am a set of three words, all with the same six letters.
First I am a kingdom, though not royally so.
Then spell me backwards, and I become a thin plate.
Now rearrange my consonants, leaving my vowels in place ...
I am now a type of paper.
What are the words?
There was an old woman who lived on a beach and the only food she had for her ten children was six potatoes. How did she make sure that each child had an equal share?
It can be easily calculated that the digits 0 to 9 can be arranged into 3628800 distinct ten-digit numbers.
But I also know how many of these numbers are prime.