Something doesn't work?

The Num lock should always be enabled. If it is disabled when you are attempting an alt code, it may cause errors or unexpected results in some applications. For example, Alt+4 could be interpreted as Alt +, ← which causes the browser to go back if the Num lock is disabled.
If your laptop keyboard doesn't have a separate NumPad, you should hold FN button with Alt button while typing the code.
This method does not work for Linux system, but it is possible to use Unicode.

Summation (Sum) Symbol

Summation sign is an alternative name for sigma sign. Sigma symbol stands for the total sum of multiple similar terms. The symbol takes the shape of enlarged Greek letter sigma. It instructs the person to sum the elements of an arrangement. Regular elements in the arrangement which are being summed are placed to the right side of the summation symbol.

The arrangement of the sigma sign:

The variable of summation is characterized by an index ( i ); the index is placed under the summation sign. Stopping point or the lower limit of the summation. Stopping point or the upper limit of the summation.

How to use and type Summation symbol code?

If your keyboard contains separate NumPad, you should be sure that it is enabled. If it is not, press the Num Lock key to activate it then press hold down the Alt key on the left side. Type the number that represents that character or the symbol you want to insert and then release the insert key.
For example, for the greek letter omega Ω press and hold Alt and the type 0234 and then release.
There is another method that works only for word documents. In this method, you should type the characters first then press Alt and X. For example ( 0234 + Alt + X for greek letter omega ).
If you have a keyboard that doesn't have NumPad here is what will work for you. Find the Function key ( FN ) then presses and hold the function key while holding press and release Num LK key; then release FN key. This method will activate the numeric keypad in your laptop.
Then do the same steps as in the previous example.
Notice that in IBM code you don't use 0 (Alt + 255 ) before the code which is different from the windows generator that requires to add 0 (Alt + 0255 ) before the code.

Table of Symbols and Codes

Symbol	Title / Description	Unicode	Code / HTML Code
⅀	Double-struck N-ary Summation	⅀	⅀
⎲	Summation Top	⎲	⎲
⎳	Summation Bottom	⎳	⎳
∑	N-ary Summation	∑	∑