# Clojure Euler: Problem 007

By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.

What is the 10001st prime number?

It’s also pretty clear problem to make you more familiar with prime numbers. As I said in Clojure Euler: Problem 003, big amount of Project Euler problems devoted to prime numbers so it is MUST HAVE (I don’t like this phrase either)

You need to implement by yourself effective prime number algorithm. And only after that use one from library. As we do.

``````(:use [clojure.contrib.lazy-seqs :only (primes)])
``````

This line import just one symbol `primes` to your namespace. It’s a prime numbers lazy sequence. Lazy sequences briefly covered in Clojure Euler: Problem 002 or Wikipedia article, that’s enough for now.

What is the 10001st prime number?

No problem.

``````(last (take 10001 primes))
``````

Two lines of code: one for import, one for solution. What can be simpler?

Note, that last return last element of the sequence and works in linear time.

Another one problem solved in few seconds minutes.

GitHub

P.S. Actually, I lied. In linked solution I use 6 lines of code: namespace declaration, use, empty line, comment with executing time, function declaration and, finally, solution.

20 November 2012