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Lesson 19 of 20 · about 15 min

Fermat's little theorem and fast powers

What's the remainder of 7 to the power 1000, divided by 13? The number itself has 846 digits, yet you can answer in your head. Powers on a clock go round in circles, and a trick called repeated squaring computes giant powers in a few dozen steps. Both are the engine of RSA.

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In this lesson you'll learn:

  • Fermat's little theorem
  • Repeated squaring

Free to try in F06 Discrete Math:

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