This has cost me almost an hour of my precious study time.

The factorial function will give wrong results from exactly 13 on.

I.e. 

factorial (12) = 12*11*10*9*8*7*6*5*4*3*2*1 = 479001600

That is just fine. 

But from 13 on, the result seems to pass a limit or whatver and gives back a wrong result...

13*12*11*10*9*8*7*6*5*4*3*2*1
=6227020800
(the same what Wolfram Alpha would return for 13! )

but, using the factorial function

factorial(13)
=1932053504

Which is wrong.

Factorial(14) will be wrong as well...





Reproducible: Always

Steps to Reproduce:
1. Start kAlgebra
2. In the Input box type "12*11*10*9*8*7*6*5*4*3*2*1", hit Enter
3. in the input box type "ans*13", hit enter
4. Now input "factorial(12)" in the input box, hit enter
5. Now input "factorial(13)" in the input box, hit enter
6. Compare results. 


Actual Results:  
Factorial function is not the same as equivalent when value is 12!.

Expected Results:  
13!  or "factorial(13)" gives the correct value

Severity: a calculator that does surprisingly give back wrong results when you dont expect it is worthless.

I had to debug a long equation step by step to find out the part with factorial(13) will give the wrong result.


Here the kAlgebra script

-------------------- save as factorial.kal and load in kAlgebra for convenience --------------
1
factorial(1)
2*1
factorial(2)
3*2*1
factorial(3)
4*3*2*1
factorial(4)
5*4*3*2*1
factorial(5)
6*5*4*3*2*1
factorial(6)
7*6*5*4*3*2*1
factorial(7)
8*7*6*5*4*3*2*1
factorial(8)
9*8*7*6*5*4*3*2*1
factorial(9)
10*9*8*7*6*5*4*3*2*1
factorial(10)
11*10*9*8*7*6*5*4*3*2*1
factorial(11)
12*11*10*9*8*7*6*5*4*3*2*1
factorial(12)
13*12*11*10*9*8*7*6*5*4*3*2*1
factorial(13)