This command forces LaTeX to give an equation the full height it needs to display as if it were on its own line. Meaning the next equation has no integer solutions. Note that math mode ignores whitespace in fact this whole code could have been put on one line and still would have compiled correctly.
You need a double back slash to indicate a new line not a single backslash.
For example Emc2 will give Emc2. An inline expression occurs in the middle of the text. There is no alignment when using the simple equation environment. For producing an inline expression the math expression should be written between the dollar sign.