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 Question from Dinesh a student: Is there any shortcut formula for multiply series numbers. like 1x2x3x4x5.......x100 =?

Hi Dinesh,

The number $100 \times 99 \times 98 \cdot\cdot\cdot \times 2 \times 1$ is called 100 factorial and is usually written $100!$ For any positive integer $n, n!$ is defined by

$n! = n \times (n-1) \times (n-2) \times \cdot\cdot\cdot \times 1.$

There is no shortcut to calculate $n!$ For small numbers you can use Google. Try it. Type 10! into the Google search window.The numbers get large quite quickly. 15! has 13 digits and 100! has 158 digits.