David M. Burton, Elementary Number Theory (7th Edition).

• Comprehensive introduction to number theory, including perfect numbers and divisors.

Richard K. Guy, The Book of Numbers.

• Accessible exploration of beautiful properties and patterns in numbers.

Wikipedia: Continued Fraction

• https://en.wikipedia.org/wiki/Continued_fraction
• Theory, examples, and applications of continued fractions.

Paul Zeitz, The Art and Craft of Problem Solving.

• Problem-solving strategies and number theory puzzles.

NPTEL: Introduction to Number Theory

• https://nptel.ac.in/courses/111/106/111106139/
• Video lectures and notes on number theory topics.