Sequence: smallest number greater than previous term with exactly n divisors: Difference between revisions

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 =={{header|Haskell}}==
 <lang haskell>import Text.Printf (printf)
-import Control.Monad (guard)
 sequence_A069654 :: [(Int,Int)]
-sequence_A069654 = go 1 $ (,) <*> length . divisors <$> [1..]
+sequence_A069654 = go 1 $ (,) <*> countDivs <$> [1..]
-  where
+ where
-    divisors n = [1..floor (sqrt $ realToFrac n)] >>= \x -> do
+   countDivs n = foldr f 0 [1..floor (sqrt $ realToFrac n)]
+    where
-      guard (n `mod` x == 0)
-      let y = n `div` x
+     f d r | n `mod` d == 0 = let y = n `div` d in if d == y then succ r else r+2
-      if x == y then [x] else [x,y]
+           | otherwise = r
-    go t ((n,d):xs) | d == t    = (t,n):go (succ t) xs
+   go t ((n,d):xs) | d == t    = (t,n):go (succ t) xs
-                    | otherwise = go t xs
+                   | otherwise = go t xs
 main :: IO ()