Data Validation: allow any Monday-only date

I need a formula in Data Validation that restricts the entry of a date to a/any Monday.

The entry in the screenshot below allows no "mm/dd" entry whatsoever... shown only to help explain what is desired.  Thanks in advance...
  data validation dialogue box
Berry MetzgerLean process improvement consultantAsked:
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telyni19Connect With a Mentor Commented:
Change the "Allow" choice to "Formula" and enter this:

Where A1 should be the first cell in your range for data validation.
Berry MetzgerLean process improvement consultantAuthor Commented:
Thanks.  That did it!
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