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  1. import Data.List
  2.  
  3. count n = foldl (\i j-> i + div n j) 0 [1..sq] * 2 - (sq^2) -- 積がn以下になる自然数の順序対の個数
  4.   where sq = floor $ sqrt $ fromIntegral n
  5.  
  6. f 0 = 0
  7. f m = f (m-1) + count (m^2 `div` 4)
  8.  
  9. main = mapM_ (print.f.read).lines =<< getContents
  10.  
Success #stdin #stdout 0.44s 4780KB
comments (?)
stdin
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20
67
125
1879
2615
3000
stdout
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3032
167672
1280414
7291768620
20635666540
31773763314
https://ideone.com/78zzrd
language:
Haskell (ghc 8.4.4)
created:
8 years ago
visibility:
public

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