I love the The Mathematics Calendar 2018.
It has an equation or other statement about math for every day, often linked to that day (like, the January 13th entry is “the sixth prime number”). Some entries are little mat quizzes for you to fugue out. Some are funny jokes, like the entry for Thanksgiving (any guesses as to what that might be? Hint: It is a formula.) The level of difficulty of understanding the reference or solving the problem ranges from suitable for a smart 7 year old (Huxley has figured some out) up through college level. Also, the picture that go with each moth are totally cool and, of course, mathy.
The calendar is complied by Rebecca Rapoport, of Harvard. She is also the author of Math Lab for Kids, which is not a dog, but a book, that looks good but that I’ve not seen.
I’m tagging this post with the keyterm “holiday shopping” to hopefully remind me to remind you that this is a great holiday gift for that special math nerd or math teacher in your life.