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chain :: Integer -> [Integer]
chain 1 = [1]
chain n
| even n = n : chain (n `div` 2)
| odd n = n : chain (n * 3 + 1)
numLongChains :: Int
numLongChains = length (filter isLong (map chain [1..100]))
where isLong xs = length xs > 15
main = do
print $ chain 10
print $ numLongChains
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