days of the week vs days ofa week

Some examples from the web:

• These are blister packs showing the days of the week.
• He renamed the days of the week.
• All you got to do is sing the days of the week and be famous.
• We need to get you one of those pill organizers with the days of the week on it.
• He didn't know what a burr hole was and he messed up the days of the week.
• Well, it's Tuesday, and I know how you forget to eat breakfast on Tuesdays 'cause the first few days of the week tend to confuse you.
• (the days of the week will be printed on the foil in abbreviated form).
• A reliable source later informed me that these double checks are applied on certain days of the week at Terminal 1B for flights to the following EU countries: Bulgaria, Poland and Romania.
• I even saw you in your underwear with the days of the week on them.
• A man has seven lives, as many as the days of the week.
• I mean, I know the days of the week, the capital of nebraska, but nothing about me.
• So, you call them days of the week?
• Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday and holiday are the days of the week.
• [Abbreviation for 7 days of the week.]
• The back of the blister pack is marked with the days of the week to help you check that you have taken a dose each day.
• They're these little pills, maybe 21 of them, days of the week written next each one?
• As you can see, today the class is learning the days of the week and the months of the year.
• I picked up your prescriptions, and I got you a little pillbox here that has all the days of the week on it so you won't even have to think about it.
• But you can't remember that, or the days of the week or the names of prisoners you met five minutes ago.
• Mark the schedule you plan to follow and remember always to change your patch on the same two days of the week you have chosen on your calendar.

Some examples from the web:

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