Career
One of his major interests is prime number theory. He is best known for results on gaps between primes and the greatest prime factor of p + a, as well as his lower bound for the number of Carmichael numbers up to X. His monograph entitled Prime-detecting Sieves was published by Princeton University Press. He has also written a book entitled Metric Number Theory, and he has in addition contributed to the field of Diophantine approximation.
Harman retired at the end of 2013 from being a professor at Royal Holloway, University of London.
Previously he was a professor at Cardiff University. Harman is married, and has three sons, and used to live in Wokingham, Berkshire before moving to Harrow, Middlesex/Greater London.