Calculate Landau's function

Wolfram Language (Mathematica), 44 bytes

Max[PermutationOrder/@Permutations@Range@#]&

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Wolfram Language (Mathematica), 31 bytes

@DanielSchepler has a better solution:

Max[LCM@@@IntegerPartitions@#]&

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05AB1E, 6 bytes

Åœ€.¿Z

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    Ŝ       # integer partitions of the input
      €.¿    # lcm of each
         Z   # maximum

Haskell, 44 bytes

(%1)
n%t=maximum$t:[(n-d)%lcm t d|d<-[1..n]]

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