From Mathisfun! Find all the factors of a number or use their Prime Factorisation Tool.
WolframAlpha queries:
Find all the factors of a number
Write a number as a product of its prime factors
Highest common factor (greatest common divisor) of two numbers
Lowest common multiple of two numbers
On Math Playground you can learn how to use factor trees to write a number as a product of its prime factors, also to find the HCF and LCM of two numbers.
The highest common factor (GCF) of 24 and 100 is 4 (2×2)
and the lowest common multiple is 600 (2×3×2×2×5×5)
(Note that you can select Help for explanations).
From Jeffrey Ventrella try this wonderful Composite Number Tree – I have used this successfully with many students. It makes a great starter. Students can watch the tree grow and work out how the tree is being formed. Ask students to comment on any patterns they notice.