Paul Erdős was a prolific writer of letters as well as articles. Along with many other mathematicians in areas such as number theory, combinatorics, and set theory, I was on his “mailing list.“ Paul’s letters arrived several times a year from mathematics centers near and far. They typically began,
I hope you are well and things are OK in Samland. I am visiting A right now, and leave next week to preach in B. Let f(n) be a function
… . This article reviews some of the topics we discussed: estimates of prime number counts, distribution questions for the Euler φ function, and elementary methods in prime number theory.