# Category Archives: number theory

## Four formats for Fermat

In my previous post I mentioned Fermat’s Little Theorem, a beautiful, fundamental result in number theory that underlies lots of things like public-key cryptography and primality testing. (It’s called “little” to distinguish it from his (in)famous Last Theorem.) There are … Continue reading

Posted in number theory, primes, proof | Tagged , , | 3 Comments

## New baby, and primality testing

I have neglected writing on this blog for a while, and here is why: Yes, there is a new small human in my house! So I won’t be writing here regularly for the near future, but do hope to still … Continue reading

Posted in meta, number theory, primes | Tagged , , , | 10 Comments

## The curious powers of 1 + sqrt 2: recurrences

In my previous post, we found an answer to the question: What’s the 99th digit to the right of the decimal point in the decimal expansion of ? However, the solution depended on having the clever idea to add . … Continue reading

Posted in number theory, puzzles | Tagged , , , , , | 8 Comments

## The curious powers of 1 + sqrt 2: a clever solution

Recall that we are trying to answer the question: What’s the 99th digit to the right of the decimal point in the decimal expansion of ? In my previous post, we computed for some small and conjectured that the answer … Continue reading

Posted in number theory, puzzles | Tagged , , , , , | 2 Comments

## The curious powers of 1 + sqrt 2: conjecture

In my previous post I related the following puzzle from Colin Wright: What’s the 99th digit to the right of the decimal point in the decimal expansion of ? Let’s play around with this a bit and see if we … Continue reading

Posted in number theory, puzzles | Tagged , , , , , | 3 Comments

## The curious powers of 1 + sqrt 2

Recently on mathstodon.xyz, Colin Wright posted the following puzzle: What’s the 99th digit to the right of the decimal point in the decimal expansion of ? Of course, it’s simple enough to use a computer to find the answer; any … Continue reading

Posted in challenges, number theory, puzzles | Tagged , , , | 15 Comments

## The Riemann zeta function and prime numbers

In a previous post I defined the famous Riemann zeta function, Today I want to give you a glimpse of what it has to do with prime numbers—which is a big part of why it is so famous. Consider the … Continue reading

Posted in number theory | Tagged , , , , | 15 Comments

## The Basel problem

I wanted to follow up on something I mentioned in my previous post: I claimed that At the time I didn’t know how to prove this, but I did some quick research and today I’m going to explain it! It … Continue reading

Posted in infinity, number theory | Tagged , , , , , | 9 Comments

## The Riemann zeta function

Recall from my previous post that given a function , we define , the Dirichlet generating function of , by We also proved that : the product of Dirichlet generating functions is the Dirichlet generating function of the Dirichlet convolution. … Continue reading

Posted in number theory | | 2 Comments

## Dirichlet generating functions

Suppose is a function defined for positive integers . Then we can define an infinite series as follows: (This might look a bit strange, but bear with me!) For example, suppose for all . Then (Note that in this case, … Continue reading

Posted in number theory | | 5 Comments