How to code the air quality health index formula in arduino

AQHI = 1000/10.4*[(e ^0.000871 * NO2 -1+ e ^0.000537 * O3 -1 + e ^0.000487 * PM2.5 -1)

Can someone explain what is e in this formula and what is its value and how to code it in Arduino?

Thank You

e means the base of the natural logarithm -- google "natural logarithm" for the whole story.
e^x means e to the power of x.

AVR libc has an exp() function that does this -- avr-libc: <math.h>: Mathematics

You can also use the Arduino pow() function to do this -- pow() - Arduino Reference
The numerical value of e is about 2.7182818284590452354