Saturday, August 30, 2008

Back to baroque numbers?

The classical, standard name for my term baroque numbers is pluperfect or polyperfect
numbers or similar. A natural number n (n = 1 2 ...) is called baroque when the sum sd(n) of all natural divisors of n is divisible by n; let's call

brq(n) := sd(n)/n

the baroqueness of n. When a baroqueness of a number is two, brq(n) = 2, then it is called perfect. The smallest perfect number, known since the ancient times, is n=6. Indeed, in this case

sd(n) = 1+2+3+4+6 = 12 = 2*n

Questions about the baroque numbers are among the oldest, open (unresolved) problems of the whole mathematics. They are difficult and, today, somewhat isolated from the main developments, hence they are not as popular among the best mathematicians as they used to be in the past, when Euclid, Fermat, Decart, Euler and others were interested in them. Let me list the main open questions:
  • are there infinitely many perfect numbers?
  • are there infinitely many baroque numbers?
  • does there exist an odd perfect number?
  • does there exist an odd baroque number > 1?
Of course n=1 is the only number for which brq(n) = 1.

The Euclid-Euler tandem (:-) proved that an even natural number n is perfect if and only if there exists a (unique) natural number p such that the following two conditions hold:
  • 2p - 1 is prime;
  • n = 2p-1*(2p-1)
It is well known and easy to see that when 2p-1 is prime then so must be the exponent p itself.

Another old result (an ancient observation) is that brq(120) = 3, i.e. 120 is a baroque number, and its baroqueness is 3.

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