Primes whose sum of digits is 25: Difference between revisions

=={{header|Haskell}}==

<lang haskell>import Data.Bifunctor (second)

import Data.List (replicate)

import Data.List.Split (chunksOf)

import Data.Numbers.Primes (primes)

--------- PRIMES WITH DECIMAL DIGITS SUMMING TO 25 -------

matchingPrimes :: [Int]

matchingPrimes =

takeWhile

(< 5000)

[n | n <- primes, 25 == decimalDigitSum n]

decimalDigitSum :: Int -> Int

decimalDigitSum n =

snd $

until

((0 ==) . fst)

(\(n, x) -> second (+ x) $ quotRem n 10)

(n, 0)

--------------------------- TEST -------------------------

main :: IO ()

main = do

let w = length (show (last matchingPrimes))

mapM_ putStrLn $

( show (length matchingPrimes)

<> " primes (< 5000) with decimal digits totalling 25:\n"

) :

( unwords

<$> chunksOf

4

(justifyRight w ' ' . show <$> matchingPrimes)

)

justifyRight :: Int -> Char -> String -> String

justifyRight n c = (drop . length) <*> (replicate n c <>)</lang>

{{Out}}

<pre>17 primes (< 5000) with decimal digits totalling 25:

997 1699 1789 1879

1987 2689 2797 2887

3499 3697 3769 3877

3967 4597 4759 4957

4993</pre>