Sum of the first n factorials

[ssayani87]

Hi guys,

I'm trying to find a way to code this formula:

Sum (from 1 to k) of n!

So, for example, Sum(1 to 4) of n! = 1! +2! +3! +4! = 24

In other words, taking sums of the factorial function where the inputs lie in a specified range. Any thoughts or advice would be greatly appreciated!

[Andrew-R]

Well you could use:

=SUM(FACT(ROW(1:4)))

Confirmed with Ctrl-Shift-Enter

Where the row numbers (1 and 4 in this case) represent the start and end points of your range.

However, are you sure this is what you want?

1!=1=1
2!=1*2=2
3!=1*2*3=6
4!=1*2*3*4=24

Therefore SUM of 1! - 4! = 1+2+6+24 = 33

[ssayani87]

Hi Andrew,

I tried out the formula you posted in the response and although it works pretty well, I think it's taking the range reference in the row function from the row numbers themselves; I was wondering if I could find a way to calculate factorials using individual cell references. So, for example, let's say i type the formula =(1+3) in cell A1, and I want my factorial function to go something like this:

=sum(fact(1:A1))

I've been trying to find a way to specify a numerical range using cell references, but no luck so far. I only need to take ranges over positive sequential integers in this case.

Thanks!

[ssayani87]

Hi Andrew,

Thanks for your help. And yes, you are correct; I incorrectly calculated the sum of the first 4 factorials in the original post. I accidentally put 4! in place of SUM of 1! - 4!.

Thanks again; I'll try out the formula and get back to you if I can't get it working.

[shg]

=sumproduct(fact(row(indirect("1:" & A1))))