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A359910
Number of odd-length integer factorizations of n into factors > 1 with the same mean as median.
14
0, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1
OFFSET
1,8
COMMENTS
The median of a multiset is either the middle part (for odd length), or the average of the two middle parts (for even length).
EXAMPLE
The a(n) factorizations for n = 120, 960, 5760, 6720:
120 960 5760 6720
4*5*6 2*16*30 16*18*20 4*30*56
2*6*10 4*12*20 3*5*6*8*8 10*21*32
8*10*12 4*4*6*6*10 12*20*28
3*4*4*4*5 2*2*8*10*18 4*5*6*7*8
2*2*2*4*4*5*9 2*4*7*10*12
2*2*2*4*5*6*7
MATHEMATICA
facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];
Table[Length[Select[facs[n], OddQ[Length[#]]&&Mean[#]==Median[#]&]], {n, 100}]
CROSSREFS
The version for partitions is A359895, ranked by A359891.
This is the odd-length case of A359909, partitions A240219.
A001055 counts factorizations.
A326622 counts factorizations with integer mean, strict A328966.
Sequence in context: A295658 A307427 A318672 * A368168 A359411 A367516
KEYWORD
nonn
AUTHOR
Gus Wiseman, Jan 24 2023
STATUS
approved