A Really Big Number

This week’s Car Talk puzzler has me stumped.

A student is asked if the following number is a perfect square: 334,912,740,121,562. Crusty knows the answer immediately. What does Crusty know?


6 Responses to A Really Big Number

  1. brianbunton says:

    Bah. I finally got it. But how long will it take you? (Credit where it’s due: my friend Rob told me the answer. Thanks!)

  2. jd2718 says:

    Ah, I arrived too late. Last digit mathematics is fun.

    Any number, raised to the fifth power… well, if you like playing with this stuff you’ll have fun. Elsewise just ignore it.


    (my mother was on car talk once. I think they suggested a new husband. Funny guys. But if changing the clutch didn’t work, gotta try changing something else, right?)

  3. not a Duke grad says:

    You’re giving Duke a bad name! This should not be a stumper. Basic perfect square rule: if it doesn’t end in 0, 1, 4, 5, 6, 9, or 0, it’s not a perfect square.

  4. brianbunton says:

    Or zero!

  5. adawes says:

    Don’t forget zero… and go Duke!

  6. brianbunton says:

    This post is getting a lot of traffic. Maybe because if you put the titular number into Google, you get two results: Car Talk’s website, and us.

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