[1]
Jim Tattersall, Elementary Number Theory in Nine Chapters, Cambridge University Press, (2005) (Website)
54
www.cambridge.org/us/academic/subjects/mathematics/number-theory/elementary-number-theory-nine-chapters-2nd-edition?format=PB
Note.
Oodles of class-tested historical material and many, many exercises, including a welter of them on topics surrounding amicable numbers.