I have read the first seven chapters of Julian Havil’s Gamma, mostly on the bus to and from work (a benefit of public transportation that does not get nearly enough attention, IMHO). It is slow going because I am working through all the mathematical derivations. These are very clearly presented so this is going well, but it still takes time. A couple modern proofs by Paul Erdös left my head spinning, but I have been able to follow (with appropriate awe), the classic results of Leonard Euler. I suppose this is appropriate given my historical interests :-)>