Add basic Project Euler solutions

project-euler-haskell/problem1.hs

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+fn :: Integer -> Integer 
+fn n | n < 3 = 0
+     | n == 3 = 3
+     | n `rem` 3 == 0 || n `rem` 5 == 0 = n + fn (n-1)
+     | otherwise = fn (n-1)
+main = do 
+   putStrLn "The sum of the multiples of 3 and 5 from 1 to 1000 is:"  
+   print (fn 1000)
+
+-- filter (\n -> n \`rem\` 3 == 0)

project-euler-haskell/problem2.hs

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+fn :: Integer -> Integer -> Integer -> Integer
+fn m n max | m == 0 = fn n 1 max
+           | sum >= max = 0
+           | even sum = sum + fn n sum max
+           | odd sum = fn n sum max
+           | otherwise = 0
+    where sum = m+n
+main = do 
+   putStrLn "The sum of the even Fibonacci numbers below 4000 is:"  
+   print (fn 0 0 4000)

project-euler-haskell/problem3.hs

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+fn :: Integer -> Integer -> Integer
+fn n fact | fact == 0 = fn n 2
+          | n `rem` fact == 0 = fn div fact
+          | fact <= 2 && fact <= div = fn n (fact+1)
+          | fact <= div = fn n (fact+2)
+          | otherwise = n
+    where div = n `quot` fact
+main = do 
+   putStrLn "The largest prime factor of 600851475143 is:"  
+   print (fn 600851475143 0)