Primes whose first and last number is 3: Difference between revisions
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Found 2,251 primes under 1,000,000 which begin and end with 3. |
Found 2,251 primes under 1,000,000 which begin and end with 3. |
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</pre> |
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=={{header|Haskell}}== |
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<syntaxhighlight lang="haskell"> |
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isPrime :: Int -> Bool |
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isPrime n |
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|n == 2 = True |
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|n == 1 = False |
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|otherwise = null $ filter (\i -> mod n i == 0 ) [2 .. root] |
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where |
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root :: Int |
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root = floor $ sqrt $ fromIntegral n |
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condition :: Int -> Bool |
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condition n = isPrime n && head numstr == '3' && last numstr == '3' |
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where |
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numstr :: String |
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numstr = show n |
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solution :: [Int] |
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solution = filter condition [1..3999] |
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main :: IO ( ) |
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main = do |
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print solution |
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putStrLn ( "There are " ++ ( show $ length $ filter condition [1..999999] |
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) ++ " 3 x 3 primes below 1000000!" ) |
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</syntaxhighlight> |
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{{out}} |
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<pre> |
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[3,313,353,373,383,3023,3083,3163,3203,3253,3313,3323,3343,3373,3413,3433,3463,3533,3583,3593,3613,3623,3643,3673,3733,3793,3803,3823,3833,3853,3863,3923,3943] |
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There are 2251 3 x 3 primes below 1000000! |
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</pre> |
</pre> |
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