Very interesting, primes fascinate me, especially the works of Riemann and the zeta function, in fact the book by John Derbyshire (Prime Obsession) is really a brilliant book if you are interested in the Reinman hypothesis (you will be if you read that book). The sieve of Eratosthenes as a start of prime number finding between limits is very good (and very efficient) and really interesting as well, those Greeks were pretty amazing in their thinking.
There are many issues with RSA and prime number based crypto, in fact a TED talk a while back showed that something like $5 Amazon time could break several thousand 512 bit keys. 1024 was a few hundred dollars at that time, but discreet log maths is really moving forward to make all of that even simpler/cheaper. The talk was great actually as Amazon time (cost) is a good measure of crypto security as it would have been in early bitcoin / blockchain when cpu was enough, in any case these are great measurements as they show the cost of an attack very well.
Your shows are great though @fergish always interesting and your hosting is superb, lets the guest talk but you keep it moving on really nicely.