

A211391


The number of divisors d of n! such that d < A000793(n) (Landau's function g(n)) and the symmetric group S_n contains no elements of order d.


1



0, 0, 0, 0, 0, 0, 2, 2, 2, 6, 4, 15, 15, 24, 29, 33, 63, 55, 126, 117, 110, 103, 225, 212, 288, 282, 319, 428, 504, 774, 859, 943, 924, 1336, 1307, 1681, 1869, 2097, 2067, 2866, 3342, 3487, 5612, 5567, 5513, 5549, 9287, 9220, 11594, 11524, 11481, 11403, 18690
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OFFSET

1,7


COMMENTS

This sequence gives the number of divisors d of S_n such that d < Lambda(n) (where Lambda(n) = the largest order of an element in S_n) for which S_n contains no element of order d. These divisors constitute a set of 'missing' element orders of S_n.
For computational purposes, the smallest divisor d0(n) of n! = S_n for which S_n has no element of order d0(n) is the smallest divisor of n! which is not the least common multiple of an integer partition of n. Thus d0(n) is given by the smallest prime power >= n+1 that is not prime (with the exception of n = 3 and 4, for which d0(n) = 6).


LINKS



EXAMPLE

For n = 7, we refer to the following table:
Symmetric Group on 7 letters.
# of elements of order 1 > 1
# of elements of order 2 > 231
# of elements of order 3 > 350
# of elements of order 4 > 840
# of elements of order 5 > 504
# of elements of order 6 > 1470
# of elements of order 7 > 720
# of elements of order 8 > 0
# of elements of order 9 > 0
# of elements of order 10 > 504
# of elements of order 12 > 420
(All other divisors of 7! > 0.)
So there are two missing element orders in S_7, whence a(7) = 2.


PROG

(Magma)
for n in [1..25] do
D := Set(Divisors(Factorial(n)));
O := { LCM(s) : s in Partitions(n) };
L := Max(O);
N := D diff O;
#{ n : n in N  n lt L };
end for;


CROSSREFS

d0(n) is equal to A167184(n) for n >= 5.


KEYWORD

nonn


AUTHOR



EXTENSIONS



STATUS

approved



