The abundancy of a positive integer 
is defined as the ratio 
, where 
is the divisor function.
For 
, 2, ..., the first few values are
1, 3/2, 4/3, 7/4, 6/5, 2, 8/7, 15/8, 13/9, 9/5, 12/11, 7/3, 14/13, ... (OEIS A017665
and A017666).
The positive integers with integer abundancy begin 1, 6, 28, 120, 496, 672, 8128, 30240, 32760, ... (OEIS A007691), corresponding to the abundancies 1, 2, 2, 3, 2, 3, 2, 4, 4, ... (OEIS A054030). The only positive integer with abundancy 1 is 1. Numbers with abundancy 2 are perfect numbers, and those with integer abundancy greater than 2 are multiperfect numbers.
