Landau's function g(n) is defined for every natural number n to be the largest order of an element of the symmetric group S_n. Equivalently, g(n) is the largest least common multiple of any partition of n.

For instance, 5 = 2 + 3 and lcm(2,3) = 6. No other partition of 5 yields a bigger lcm, so g(5) = 6. An element of order 6 in the group S₅ can be written in cycle notation as (1 2) (3 4 5).

The integer sequence g(0) = 1, g(1) = 1, g(2) = 2, g(3) = 3, g(4) = 4, g(5) = 6, g(6) = 6, g(7) = 12, g(8) = 15, ... is A000793.

The sequence is named after Edmund Landau, who proved that

(where ln denotes the natural logarithm).

The following recursive formula can be used to compute g(n):

External links

On-Line Encyclopedia of Integer Sequences: Sequence A000793, Landau's function on the natural numbers.