This is a set of Project Euler solutions in which no programming language is
used twice.

Each program begins with a comment containing the entire problem description.
When run, each program prints the solution and a single newline to standard
output.

Programs are each a single source file named `nnn.ext`.  (Unless they're not —
see XSLT.) Most can be compiled/run by giving the filename to a standard
compiler/interpreter.  For esoteric runtimes (consider vimscript), the source
may contain brief instructions on how to get the code to run, but this is only
done when absolutely necessary.

Note that when it matters, a POSIX-compatible shell is assumed, because I'm
running Linux.


# Rules

The rules are loose and entirely subject to my interpretation, but I try to
stick to the following:

* Languages may not be reused.  Variants are generally avoided, but the
  ultimate guideline is whether the result would be _interesting_.

* Languages shall be chosen without regard for the requirements of the next
  problem.  Ideally, I should have no idea what the next problem even is.

* Trivial transformational scripts (in any language) are allowed in extreme
  cases if a language is particularly difficult to read or write.  This
  exception exists solely for Whitespace.

* Programs must perform the actual calculation.  The general pattern is that
  any numbers or other parameters that appear in the problem are defined as
  constants within the program; changing the constants thus ought to produce
  the appropriate answer.  (Programs are not, however, expected to deal with
  excessively large or malformed parameters.)


# Languages used

* Problem 1: Ruby  
    _Add all the natural numbers below one thousand that are multiples of 3 or 5._

* Problem 2: C  
    _By considering the terms in the Fibonacci sequence whose values do not exceed four million, find the sum of the even-valued terms._

* Problem 3: C++  
    _Find the largest prime factor of a composite number._

* Problem 4: x86 assembly  
    _Find the largest palindrome made from the product of two 3-digit numbers._

* Problem 5: Brainfuck  
    _What is the smallest number divisible by each of the numbers 1 to 20?_

* Problem 6: Whitespace  
    _What is the difference between the sum of the squares and the square of the sums?_

* Problem 7: MUMPS  
    _Find the 10001st prime._

* Problem 8: vimscript  
    _Discover the largest product of five consecutive digits in the 1000-digit number._

* Problem 9: LOLcode  
    _Find the only Pythagorean triplet, {a, b, c}, for which a + b + c = 1000._

* Problem 10: Standard ML  
    _Calculate the sum of all the primes below two million._

* Problem 11: Bash  
    _What is the greatest product of four adjacent numbers on the same straight line in the 20 by 20 grid?_

* Problem 12: Prolog  
    _What is the value of the first triangle number to have over five hundred divisors?_

* Problem 13: Lua  
    _Find the first ten digits of the sum of one-hundred 50-digit numbers._

* Problem 14: XSLT  
    _Find the longest sequence using a starting number under one million._

* Problem 15: COBOL  
    _Starting in the top left corner in a 20 by 20 grid, how many routes are there to the bottom right corner?_

* Problem 16: Pascal  
    _Power digit sum_

* Problem 17: Inform7  
    _Number letter counts_

* ...

* Problem 67: Haskell  
    _Using an efficient algorithm find the maximal sum in the triangle?_

## Declared unusable

For posterity, the following languages have been attempted in the past, but
have been ruled _unusable_ by executive decree.

* Malbolge


# Links

* [Project Euler](http://projecteuler.net/)
* [Full list of Project Euler problems](http://projecteuler.net/problems)
* [Blog series about these solutions](http://me.veekun.com/blog/categories/project-euler/)