Data commit

Task/Smarandache-prime-digital-sequence/Haskell/smarandache-prime-digital-sequence.hs

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+{-# LANGUAGE NumericUnderscores #-}
+import Control.Monad (guard)
+import Math.NumberTheory.Primes.Testing (isPrime)
+import Data.List.Split (chunksOf)
+import Data.List (intercalate)
+import Text.Printf (printf)
+
+smarandache :: [Integer]
+smarandache = [2,3,5,7] <> s [2,3,5,7] >>= \x -> guard (isPrime x) >> [x]
+ where s xs = r <> s r where r = xs >>= \x -> [x*10+2, x*10+3, x*10+5, x*10+7]
+
+nextSPDSTerms :: [Int] -> [(String, String)]
+nextSPDSTerms = go 1 smarandache
+ where
+  go _ _ [] = []
+  go c (x:xs) terms
+   | c `elem` terms = (commas c, commas x) : go nextCount xs (tail terms)
+   | otherwise      = go nextCount xs terms
+   where nextCount = succ c
+
+commas :: Show a => a -> String
+commas = reverse . intercalate "," . chunksOf 3 . reverse . show
+
+main :: IO ()
+main = do
+  printf "The first 25 SPDS:\n%s\n\n" $ f smarandache
+  mapM_ (uncurry (printf "The %9sth SPDS: %15s\n")) $
+    nextSPDSTerms [100, 1_000, 10_000, 100_000, 1_000_000]
+ where f = show . take 25