geowa4

euler6 :: Int
euler6 = a - b
  where
    a = (^2) $ sum [1..100]
    b = sum [x^2 | x <- [1..100]]

geowa4

leastDivisor :: Integer -> Integer -> Integer
leastDivisor divisor n
  | rem n divisor == 0 = divisor
  | divisor^2 > n      = n
  | otherwise          = leastDivisor (divisor+1) n

hasFactor :: Integer -> Bool
hasFactor 1 = False
hasFactor n = (leastDivisor 2 n) /= n

geowa4

import Data.Char (digitToInt)
import Data.List (tails)

euler8 :: Int
euler8 = maximum $ map (product . take 5) (tails number)
  where
    str = "73167176531330624919225119674426574742355349194934\
          \96983520312774506326239578318016984801869478851843\
          \85861560789112949495459501737958331952853208805511\
          \12540698747158523863050715693290963295227443043557\

geowa4

euler9 :: Int
euler9 = floor $ head [a * b * c | b <- [1..998], a <- [1..b], let c2 = a^2 + b^2, let c = sqrt c2, a + b + c == 1000, a^2 + b^2 == c2]

geowa4

leastDivisor :: Integer -> Integer -> Integer
leastDivisor divisor n
  | rem n divisor == 0 = divisor
  | divisor^2 > n      = n
  | otherwise          = leastDivisor (divisor+1) n

hasFactor :: Integer -> Bool
hasFactor 1 = False
hasFactor n = (leastDivisor 2 n) /= n

geowa4

import Data.List (group)

leastDivisor :: Integer -> Integer -> Integer
leastDivisor divisor n
  | rem n divisor == 0 = divisor
  | divisor^2 > n      = n
  | otherwise          = leastDivisor (divisor+1) n

factors :: Integer -> [Integer]
factors 1 = []

geowa4

euler13 :: String
euler13 = (take 10) . show . sum $ nums

nums :: [Integer]
nums = [37107287533902102798797998220837590246510135740250,
        46376937677490009712648124896970078050417018260538,
        74324986199524741059474233309513058123726617309629,
        91942213363574161572522430563301811072406154908250,
        23067588207539346171171980310421047513778063246676,

geowa4

import Data.List (foldl')

collatz :: Int -> [Int]
collatz n
  | n == 1    = [1]
  | even n    = n : collatz (n `div` 2)
  | otherwise = n : collatz (3 * n + 1)

compareCollatzTuple :: (Int, Int) -> Int -> (Int, Int)
compareCollatzTuple acc x =

geowa4

import Data.Char (digitToInt)

euler16 :: Int
euler16 = sum $ map digitToInt (show (2^1000))

geowa4

import Data.Char (digitToInt)

factorial :: (Integral a) => a -> a  
factorial 0 = 1  
factorial n = n * factorial (n - 1)

euler20 :: Int
euler20 = sum . (map digitToInt) . show . factorial $ 100