Idoneal Number

Author

Eric W. Weisstein
March 12, 2004

This notebook downloaded from http://mathworld.wolfram.com/notebooks/IntegerSequences/IdonealNumber.nb.

For more information, see Eric's MathWorld entry http://mathworld.wolfram.com/IdonealNumber.html.

©2005 Wolfram Research, Inc. except for portions noted otherwise

Code

Developer`SetSystemOptions["ReduceOptions"->{"DiscreteSolutionBound"->10000}];

IdonealQ[n_Integer]:=Reduce[a b+b c+c a==n&&0<a<b<c&&(a|b|c)∈Integers,{a,b,c}]===False

Enumeration

Position[Range[100],_?IdonealQ]//Flatten//Timing

Position[Range[1000],_?IdonealQ]//Flatten//Timing

Position[Range[1000],_?IdonealQ]//Flatten//Timing

Position[Range[5000],_?IdonealQ]//Flatten//Timing