abundancy ( n ) = abund ( n ) = sum-of-divisors ( n ) / n
It's the concept underlying perfect numbers , multiperfect numbers , friendly numbers , abundant numbers and deficient numbers .
Abundancy "Outlaws" of the Form sigma(N)+t / N
Journal of Integer Sequences, Vol. 10(2007), Article 07.9.6 , pp. 1-19 ,
William G. Stanton and Judy A. Holdener presented a table of abundancies and non-abundancies .
This table was extended to 2^34 in Augmentation of Table of Abundancies .
Michel Marcus has kindly excerpted his extensive on-going calculations , providing a list of abundancies in Extended Table of Abundancies , updated 2012-01-30 .
There is a bibliography of abundancy at Abundancy , some resources .
2010 Mathematics Subject Classification : Primary 11A25 ;
Secondary 11A05 , 11A41 , 11A51 , 11N25 , 11N60 , 11Y05 , 11Y55 , 11Y70