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The Excel SERIESSUM Function
Basic Description
The Excel SERIESSUM function returns the sum of a power series, based on the following power series expansion:
The syntax of the function is :
SERIESSUM( x, n, m, coefficients )
Where the function arguments are:
x    The input value to the power series 
n    The initial power, to which x is to be raised 
m    The step size that n is increased by, on each successive power of x 
coefficients    An array of coefficients that multiply each successive power of x 
The number of values in the supplied coefficients array defines the number of terms in the power series. This is illustrated in the following example.
Excel Seriessum Function Examples
Example 1
In the example below, the Excel Seriessum function is used to calculate the power series:
5^{1} + 5^{2} + 5^{3} + 5^{4} + 5^{5}
Formulas:  A 

1  =SERIESSUM( 5, 1, 1, {1,1,1,1,1} ) 

 Results: 
Example 2
In the example below, the Excel Seriessum function calculates the power series:
1 * 2^{1} + 2 * 2^{3} + 3 * 2^{5} + 4 * 2^{7} + 5 * 2^{9}
Formulas:  A 

1  =SERIESSUM( 2, 1, 2, {1,2,3,4,5} ) 

 Results: 
More details and examples of the Excel Seriessum function are provided on the Microsoft Office website.
Seriessum Function Errors
If you get an error from the Excel Seriessum Function, this is likely to be one of the following:
Common Errors
#VALUE!    Occurs if any of the supplied arguments are nonnumeric 
#NAME?    Occurs when Analysis ToolPak addin is not enabled in your Excel. You will need to enable the addin if you want to use the Excel Seriessum function.
+ Show How to Do This in Excel 2003:
 From the Tools dropdown menu, select the option AddIns ...
 An 'AddIns' window will pop up. From this, select the option Analysis ToolPak and click OK
+ Show How to Do This in Excel 2007:
 Click the Microsoft button on the top left of your spreadsheet and select
the Excel Options button
 From the menu on the left hand side, select AddIns
 In the 'Manage:' box, select Excel Addins and click Go...
 An 'AddIns' window will pop up. From this, select the option Analysis ToolPak and click OK
+ Show How to Do This in Excel 2010 or Excel 2013:
 Click the File tab (top left of your spreadsheet) and select Options
 From the menu on the left hand side, select AddIns
 If the window that pops up doesn't show the 'Addins' list, use the 'Manage:'
dropdown menu (at the bottom of the window) to select Excel Addins. Click Go...
 From the 'AddIns' window, select the option Analysis ToolPak and click OK
