Children's non fiction book about the number 7

When I was 7 I got a non-fic book about the number 7. It had loads of facts that involved the number such as days of the week, the rainbow, and the amount of vertebrae in a giraffe's neck. I think it was a series about different numbers (I think my brother got one about 10 around the same time). I cannot for the life of me find it anywhere