# Difference between revisions of "Euler problems/51 to 60"

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[[Category:Programming exercise spoilers]] | [[Category:Programming exercise spoilers]] | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=51 Problem 51] == |

Find the smallest prime which, by changing the same part of the number, can form eight different primes. | Find the smallest prime which, by changing the same part of the number, can form eight different primes. | ||

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</haskell> | </haskell> | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=52 Problem 52] == |

Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x, contain the same digits in some order. | Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x, contain the same digits in some order. | ||

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</haskell> | </haskell> | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=53 Problem 53] == |

How many values of C(n,r), for 1 ≤ n ≤ 100, exceed one-million? | How many values of C(n,r), for 1 ≤ n ≤ 100, exceed one-million? | ||

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</haskell> | </haskell> | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=54 Problem 54] == |

How many hands did player one win in the game of poker? | How many hands did player one win in the game of poker? | ||

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</haskell> | </haskell> | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=55 Problem 55] == |

How many Lychrel numbers are there below ten-thousand? | How many Lychrel numbers are there below ten-thousand? | ||

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</haskell> | </haskell> | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=56 Problem 56] == |

Considering natural numbers of the form, a<sup>b</sup>, finding the maximum digital sum. | Considering natural numbers of the form, a<sup>b</sup>, finding the maximum digital sum. | ||

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</haskell> | </haskell> | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=57 Problem 57] == |

Investigate the expansion of the continued fraction for the square root of two. | Investigate the expansion of the continued fraction for the square root of two. | ||

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</haskell> | </haskell> | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=58 Problem 58] == |

Investigate the number of primes that lie on the diagonals of the spiral grid. | Investigate the number of primes that lie on the diagonals of the spiral grid. | ||

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</haskell> | </haskell> | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=59 Problem 59] == |

Using a brute force attack, can you decrypt the cipher using XOR encryption? | Using a brute force attack, can you decrypt the cipher using XOR encryption? | ||

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</haskell> | </haskell> | ||

− | == [http://projecteuler.net/index.php?section= | + | == [http://projecteuler.net/index.php?section=view&id=60 Problem 60] == |

Find a set of five primes for which any two primes concatenate to produce another prime. | Find a set of five primes for which any two primes concatenate to produce another prime. | ||

## Revision as of 13:51, 20 July 2007

## Contents

## Problem 51

Find the smallest prime which, by changing the same part of the number, can form eight different primes.

Solution:

```
problem_51 = undefined
```

## Problem 52

Find the smallest positive integer, x, such that 2x, 3x, 4x, 5x, and 6x, contain the same digits in some order.

Solution:

```
problem_52 = head [n | n <- [1..],
digits (2*n) == digits (3*n),
digits (3*n) == digits (4*n),
digits (4*n) == digits (5*n),
digits (5*n) == digits (6*n)]
where digits = sort . show
```

## Problem 53

How many values of C(n,r), for 1 ≤ n ≤ 100, exceed one-million?

Solution:

```
problem_53 = length [n | n <- [1..100], r <- [1..n], n `choose` r > 10^6]
where n `choose` r
| r > n || r < 0 = 0
| otherwise = foldl (\z j -> z*(n-j+1) `div` j) n [2..r]
```

## Problem 54

How many hands did player one win in the game of poker?

Solution:

```
problem_54 = undefined
```

## Problem 55

How many Lychrel numbers are there below ten-thousand?

Solution:

```
problem_55 = length $ filter isLychrel [1..9999]
where isLychrel n = all notPalindrome (take 50 (tail (iterate revadd n)))
notPalindrome s = (show s) /= reverse (show s)
revadd n = n + rev n
where rev n = read (reverse (show n))
```

## Problem 56

Considering natural numbers of the form, a^{b}, finding the maximum digital sum.

Solution:

```
problem_56 = maximum [dsum (a^b) | a <- [1..99], b <-[1..99]]
where dsum 0 = 0
dsum n = let ( d, m ) = n `divMod` 10 in m + ( dsum d )
```

## Problem 57

Investigate the expansion of the continued fraction for the square root of two.

Solution:

```
problem_57 = length $ filter topHeavy $ take 1000 convergents
where topHeavy r = numDigits (numerator r) > numDigits (denominator r)
numDigits = length . show
convergents = iterate next (3%2)
next r = 1 + 1/(1+r)
```

## Problem 58

Investigate the number of primes that lie on the diagonals of the spiral grid.

Solution:

```
problem_58 = undefined
```

## Problem 59

Using a brute force attack, can you decrypt the cipher using XOR encryption?

Solution:

```
problem_59 = undefined
```

## Problem 60

Find a set of five primes for which any two primes concatenate to produce another prime.

Solution:

```
problem_60 = undefined
```