import Data.List (elemIndex, maximumBy) 
import Data.Ord (comparing)
import Data.Maybe (fromJust)

recurringCycle :: Int -> Int
recurringCycle d = remainders 1 []
  where
    remainders r rs
      | r == 0          = 0
      | s `elem` rs     = 1 + fromJust (elemIndex s rs)
      | otherwise       = remainders ((r * 10) `mod` d) (s : rs)
      where s = r `mod` d

p26 :: Int
p26 = fst $ maximumBy (comparing snd) [(n, recurringCycle n) | n <- [1,3..999], n `mod` 5 /= 0]

λ> :set +s
λ> p26
983
(0.11 secs, 29,770,480 bytes)
λ> 

— Me@2025-02-06 08:29:54 AM

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2025.02.06 Thursday (c) All rights reserved by ACHK