2520 is
The interesting thing is, its very difficult to get to this number using mathematics.
The following incident is of particular interest:
One Day a person came to Ali (A.S.), thinking that since Ali thinks he is too smart, I'll ask him such a tough question that he won't be able to answer it and I'll have the chance to embarrass him in front of all the Arabs.
He asked "Ali, tell me a number, that if we divide it by any number from 1-10 the answer will always come in the form of a whole number and not as a fraction."
Hazrat Ali(as) Looked back at him and said, "Take the number of days in a year and multiply it with the number of days in a week and you will have your answer."
The person got astonished but as he was a Mushrik he still didn't believe Ali (A.S.). He calculated the answer Ali (AS) gave him. To his amazement he came across the following results:
The number of Days in a Year = 360 (in Arabic Calendar)
The Number of Days in a Week = 7
The product of the two numbers = 2520
Now ... 2520 / 1 = 2520
2520 / 2 = 1260
2520 / 3 = 840
2520 / 4 = 630
2520 / 5 = 504
2520 / 6 = 420
2520 / 7 = 360
2520 / 8 = 315
2520 / 9 = 280
2520 / 10= 252