How to delete all the characters in cell and leave just the numbers?

With
A1: d 123-c\ 54.348xD c541

Try this:

First, create a Named Formula....
From the Excel Main Menu: <insert><name><define>

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This ARRAY FORMULA (committed with CTRL+SHIFT+ENTER, instead of just ENTER) removes ALL non-numerics from a string

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In the example, the formula returns: 12354348541

NOTE: That formula can only return Excel's limit of 15 digits.

(Credit goes to Harlan Grove for that solution)

Well, to combine the formulas in your example.....

Try this:

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Does that help?