Sums of cubes

Calculate each of the following:

• $1^3 + 5^3 + 3^3 = ?$
• $16^3 + 50^3 + 33^3 = ?$
• $166^3 + 500^3 + 333^3 = ?$
• $1666^3 + 5000^3 + 3333^3 = ?$

What do you see? Can you state and prove a generalization of your observations?