Odd abundant number question

hv at crypt.org hv at crypt.org
Fri May 20 02:19:12 CEST 2005


Earlier I wrote:
:"David Wilson" <davidwwilson at comcast.net> wrote:
::Is an odd abundant number necessarily a sum of proper divisors of itself?
:
:Checking UPINT, I find that a number is called "pseudoperfect" if it is
:the sum of some of its proper divisors, and "weird" if it is abundant
:but not pseudoperfect [...]
:
:Below is a simple perl/PARI test script.

I can confirm there is no odd weird number less than 101,355,345.

The simple program is running pretty slowly now; I suspect a pure-PARI
(or pure-Mathematica/Maple/other) program would be able to check up to
10^9 before things started to get painful.

Note that all odd abundant numbers below about 5E9 are divisible by 3
(5^2.7.11.13.17.19.23.29 being the first counterexample), which saves
a lot of unnecessary factorisation.

Hugo





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