I found this today. If you need an odd value of resistance, it will calculate the various combinations of the 2 E24 series resistors required to make what you're looking for. It also shows the % deviation from the target value.
http://www.sengpielaudio.com/calculator-parallel.htm
This a real timesaver.
http://www.sengpielaudio.com/calculator-parallel.htm
This a real timesaver.