Odd abundant number
An odd abundant number is an odd number [math]\displaystyle{ n }[/math] that its sum-of divisors greater than the twice of itself.
Examples
- The first example is 945 (33× 5× 7). Its prime factors are 3, 5, and 7. The next following eleven odd abundant numbers are
1575, 2205, 2835, 3465, 4095, 4725, 5355, 5775, 5985, 6435, 6615.
- Odd abundant numbers below 500000 are in On-Line Encyclopedia of Integer Sequences A005231.
Formulas
The following formula
[math]\displaystyle{ 945+630n }[/math][1] presents 62 abundant numbers, but it fails if
[math]\displaystyle{ n\le62 }[/math].
The second formula
[math]\displaystyle{ 3465+2310n }[/math][2] presents 192 abundant numbers, but fails if
[math]\displaystyle{ n\le192 }[/math]
The third formula
[math]\displaystyle{ 2446903305+1631268870n }[/math] [3]
fails if [math]\displaystyle{ n\le135939073 }[/math].
Properties
- An calculation was given by Iannucci shows how to find the smallest abundant number not divisible by the first n primes.
- An abundant number with abundance 1 is called a quasiperfect number, although none have yet been found. A quasiperfect number must be an odd square number having a value above 1030.