Summation Part of Erlang C Formula

[tinydancer]

What would be the best way to write the below summation into a formula in excel?

It is part of the Erlang C formula and I am looking to calculate it a number of times. Right now I have a table that changes based on the "A" value then I use a vlookup based on "N-1" to go grab that sum. I can't build a whole table each time for a calculation I'm looking to do well over a thousand times. Looking to see if anybody has a workaround to turn this into a formula.

Thank you

 

[bobsan42]

You are aware there is a limit of the size of numbers excel can calculate accurately? Of courrse it all depends on N as well.

 

[bobsan42]

Erlang C Formula – Made Simple With an Easy Worked Example

We’ve simplified the Erlang C Formula into easy steps with a clear, worked example to help you understand and apply it effortlessly.

www.callcentrehelper.com

This guys claim to have an excel example. But I can't be bothered to check it on my phone.

 

[tinydancer]

Yes I am familiar with the link you posted and I do know n can only go to 170. I have already built an excel tool that can calculate erlang c. The summation I mentioned above though is the part I am looking to condense. So perhaps I shouldn't have mentioned erlang c as I have already solved all other issues with it, I am just looking to calculate the above summation in one formula.

 

[bobsan42]

I admit I have not looked at the example and have never needed this particular formula before, but isn't dealing with the sum part of the provided example?
I will have a look tomorrow. Past midnight is no time to deal with such problems ?.

 

[Eric W]

How about:

Book3
	A	B
1	A	N
2	5	6
3
4
5
6	91.41667
7	91.41667
Sheet1

Cell Formulas
Range	Formula
A6	A6	=SERIESSUM(A2,0,1,1/(FACT(ROW(INDIRECT("1:"&B2))-1)))
A7	A7	=SERIESSUM(A2,0,1,1/(FACT(SEQUENCE(B2,,0))))
Press CTRL+SHIFT+ENTER to enter array formulas.

A7 is if you have Excel 365.

 

[tinydancer]

How about:

Book3
	A	B
1	A	N
2	5	6
3
4
5
6	91.41667
7	91.41667
Sheet1

Cell Formulas
Range	Formula
A6	A6	=SERIESSUM(A2,0,1,1/(FACT(ROW(INDIRECT("1:"&B2))-1)))
A7	A7	=SERIESSUM(A2,0,1,1/(FACT(SEQUENCE(B2,,0))))
Press CTRL+SHIFT+ENTER to enter array formulas.

A7 is if you have Excel 365.

Your answer appears to be correct but whenever I plug in your formula all I am getting is 1. Any thoughts?

 

[bobsan42]

Did you put the numbers in A2 and B2?

 

[tinydancer]

 

[bobsan42]

You have not entered the formula as array formula.
Enter the cell with F2 the press Ctrl+Shift+Enter.