• Oscar Cunningham@lemmy.world
    0·
    7 months ago

    The Heegner Numbers. These are the n such that ℚ[√-n] has unique factorisation. There are exactly 9 of them:

    1, 2, 3, 7, 11, 19, 43, 67, 163.

    A famous fact about them is that 163 being a Heegner Number leads to e^(π√163) being very close to a whole number.

    262537412640768743.99999999999925…

  • zipsglacier@lemmy.world
    0·
    1 year ago

    There are tons of them! For example, the class of numbers n such that there is a Platonic solid made of n-gons. This class only has the numbers 3, 4, and 5. You can get other examples any time there is an interesting mathematical structure with only finitely many examples.