"excess number" is correct and usable in written English.
You can use it when you want to refer to a quantity that is greater than what is necessary or desired. For example, "The excess number of students in the classroom made it difficult for the teacher to effectively manage the class."
One of them is the excess number of houses.
"People with Lesch-Nyhan have an excess number of involuntary movements," Jinnah said.
We calculated the significance of the excess number of genes attaining the specified thresholds in two main ways.
We investigate how to exploit the excess number of thrusters to accommodate thruster faults during operation.
A good example of this is the United States Navy, which at this time has an excess number of battleships and other vessels.
The excess number of dipoles pointing with the field is determined by (mB/kT), where mB represents the magnetic energy and kT the thermal energy.
Additional data collection and analyses confirmed the excess number of deaths in patients treated with DCLHb but failed to reveal the cause of these deaths.
The planners regarded competition as wasteful because it allowed an excess number of competitors, and then forced some to close down.
The free energy change in the surface region is calculated and is used to obtain the excess number of molecular layers in the surface region.
When the magnetic energy is small compared to the thermal energy, the excess number of dipoles pointing with the field is proportional to the field and inversely proportional to the absolute temperature, corresponding to Curie's law.
Solute-solvent concentration fluctuation correlations at infinite dilution are a statistical measure of the excess number of solvent molecules surrounding a given solute molecule, with respect to a uniform distribution at the prevailing density.
