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We call a number cozy if every digit in the number is either even or next to an even digit.  For example, a number is cozy if every digit in the number is either a 2 or next to a 2.  For example, the number 222, 72, 45, and 810 and are all cozy.  Also, the numbers 202 and 2772 are cozy.

 

How many 4-digit numbers are cozy?

 Dec 20, 2023

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