The factorial of natural number is the work of all previous natural numbers, including number. The factorial of zero is equal to unit. It seems that to count a number factorial very simply – enough to multiply all natural numbers which are not exceeding set. However, the value of a factorial so quickly increases that some calculators do not cope with this task.

## It is required to you

- calculator, computer

## Instruction

1. To count a factorial of natural number multiply all natural numbers which are not surpassing this. Each number is considered only once. In the form of a formula it can be written down as follows: n! = 1*2*3*4*5 * … * (n-2) * (n-1) of *n, gden – natural number which factorial is required to be counted. 0! is accepted equal to unit (0! =1). increase of an argument the value of a factorial very quickly increases therefore the ordinary (accounting) calculator for a factorial of 15 instead of result can already give the error message.

2. To count a factorial of large natural number, take the engineering calculator. That is, such calculator on which keyboard there are designations of mathematical functions (cos, sin, √). Gather initial number on the calculator, and then press the button of calculation of a factorial. Usually such button is designated as "n!" or similarly (instead of the letter "n" there can be "N" or "x", but the exclamation mark "!" has to be present at designation of a factorial anyway). At great values of an argument the results of calculations begin to be displayed in a "exponential" (indicative) look. So, for example, the factorial 50 will be presented in shape: 3,0414093201713378043612608166065e+64 (or similar). To receive result of calculations in a usual look, attribute to the number shown to an e symbol it is so much zero how many it is specified after "e +" (if, of course, there will be enough place).

3. To count a number factorial on the computer, start the calculator program (standard Windows calculator). For this purpose find its image on a desktop or press the Start-up and Execute buttons. Then, gather in the appeared window of "calc" and press "Ok". Look: in what mode the Calculator program was started. If the picture reminds the ordinary "accounting" calculator, switch it to the "engineering" mode. For this purpose, just click a mouse on the Look point and choose the line "Engineering" in the list of options. Then, do the same actions which are listed in the previous paragraph of the instruction - gather number and press the button "n!".

4. It is possible "to count" a factorial of number and without use of computer facilities. For this purpose just print out the table of factorials. As values of a factorial very quickly increase, to really unpack only factorials of numbers from 0 to 50. However, practical application of such tables is very doubtful. First, on input of such multidigit number a lot of time will leave, secondly, mistake probability at input is high, and, thirdly, it is not absolutely clear – where to enter such long number. Neither on the display of the calculator, nor in Excel cell so many figures just will not go in.