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A perfect number is a number that is the sum of its proper divisors: 28 = 1 + 2 + 4 + 7 + 14

Is there a name for numbers whose only proper divisors are 1, 2, and N/2? For example

6 is divisible by 1, 2, and 3

8 is divisible by 1, 2, and 4

34 is divisible by 1, 2, and 17

Is there a name for these numbers?

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7  
Yes, I would call them even numbers. –  Aryabhata Oct 14 '10 at 16:43
    
Perhaps Wayne meant 34 is divisible by 17? And perhaps he also meant those are its only divisors. –  Joseph O'Rourke Oct 14 '10 at 16:48
1  
I guess you would call them even semiprimes, or 8. en.wikipedia.org/wiki/Semiprime –  Jonas Meyer Oct 14 '10 at 17:18
14  
Also known as "twice a prime, or 8". –  David Speyer Oct 14 '10 at 17:29
3  
I suppose 8 is twice a prime in the sense of Grothendieck (the same sense in which 57 is prime). –  Nate Eldredge Oct 14 '10 at 17:49

1 Answer 1

Aside from 8 and arguably 2, these are the even semiprimes, Sloane's A100484.

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