Factorial

[ctrnz]

Excel has excellent built in function FACT() which does n! calculations.
But I don't need 1*2*3*4*5. Instead I need 1+2+3+4+5 calculation.
Excel has such built in function?

Thank You,
AK

 

[barry houdini]

Hello riaz, you could tidy that up a little I think, I'd go with

=(A1-B1+1)*(A1+B1)/2

 

[riaz]

Thank you Barry. I agree it is tidier.

 

[tusharm]

One multiplication compared to one exponentation. Though, as people may have noticed I've never really been much into optimizing performance where none was needed. {grin}

More important, expandability. As Riaz pointed out n*(n+1)/2 can be easily extended to sum values from m to n with n*(n+1)/2 - (m-1)*m/2. On the other hand, (n+n^2)/2 would become (n+n^2)/2 - (m-1 + (m-1)^2)/2

Hello Tushar,

Why do you prefer that version? Is it more transparent....or is there something else?

 

[barry houdini]

Thanks for your comments, Tushar