The abundancy of a number
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).
A positive integer
for which
is an integer is called a multiperfect number.
The first few are 1, 6, 28, 120, 496, 672, 8128, ... (OEIS A007691),
corresponding to the abundancies 1, 2, 2, 3, 2, 3, 2, 4, 4, ... (OEIS A054030).
Guy, R. K. "The Second Strong Law of Small Numbers." Math. Mag.63, 3-20, 1990.Sloane, N. J. A. Sequences
A007691/M4182, A017665,
A017666, and A054030
in "The On-Line Encyclopedia of Integer Sequences."
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).
for which 
is an integer is called a multiperfect number.
The first few are 1, 6, 28, 120, 496, 672, 8128, ... (OEIS A007691),
corresponding to the abundancies 1, 2, 2, 3, 2, 3, 2, 4, 4, ... (OEIS A054030).
