A number is practical if for all , is the sum of distinct proper divisors of . Defined in 1948 by
A. K. Srinivasen. All even Perfect Numbers are practical. The number
References
Melfi, G. ``On Two Conjectures About Practical Numbers.'' J. Number Th. 56, 205-210, 1996.
Melfi, G. ``Practical Numbers.''
http://www.dm.unipi.it/gauss-pages/melfi/public_html/pratica.html.
Sloane, N. J. A. Sequence
A005153/M0991
in ``An On-Line Version of the Encyclopedia of Integer Sequences.''
http://www.research.att.com/~njas/sequences/eisonline.html and Sloane, N. J. A. and Plouffe, S.
The Encyclopedia of Integer Sequences. San Diego: Academic Press, 1995.