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

Content added Content deleted
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<lang haskell>import Data.List (nub)
<lang haskell>import Data.List (nub)
import Text.Printf (printf)
import Text.Printf (printf)
import Control.Monad (guard)


sequence_A069654 :: [(Int,Int)]
sequence_A069654 :: [(Int,Int)]
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where
where
nDivCount = (,) <*> divisorCount <$> [1..]
nDivCount = (,) <*> divisorCount <$> [1..]
divisorCount = length . nub . foldr (\(a, b) r -> a:b:r) [] . divisors
divisorCount = length . nub . divisors
where
where
divisors n = [ (x, n `div` x)
divisors n = [1..ceiling (sqrt $ realToFrac n)] >>= \x ->
| x <- [1..ceiling (sqrt $ realToFrac n)]
guard (n `mod` x == 0) >> [x, n `div` x]
, n `mod` x == 0 ]
go t ((n,d):xs)
go t ((n,d):xs)
| d == t = (t,n):go (succ t) xs
| d == t = (t,n):go (succ t) xs
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