Operator '+' cannot be applied to types 'Number' and '1'

Googling the error message leads you to https://github.com/Microsoft/TypeScript/issues/2031 which pretty much explains the reason why it does not work.

You can also have a look at the Do's and Don'ts Section:

Number, String, Boolean, and Object

Don’t ever use the types Number, String, Boolean, or Object. These types refer to non-primitive boxed objects that are almost never used appropriately in JavaScript code.

/* WRONG */
function reverse(s: String): String;

Do use the types number, string, and boolean.

/* OK */
function reverse(s: string): string;

In other words, replace the type Number with number.

Just replace Number with number wherever you are defining the type for PageIndex in your code.

Alternatively, you can try adding the unary operator + like,

CurrentPage: +this.paging.PageIndex + 1

which will also work in your case.

Hope this helps!