A370645 - OEIS

A370645

Number of integer factorizations of n into unordered factors > 1 such that only one set can be obtained by choosing a different prime factor of each factor.

1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 3, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1, 2, 2, 1, 1, 4, 1, 2, 1, 2, 1, 3, 1, 3, 1, 1, 1, 3, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 5, 1, 1, 2, 2, 1, 1, 1, 4, 1, 1, 1, 3, 1, 1, 1

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OFFSET

1,12

COMMENTS

All of these factorizations are co-balanced (A340596).

LINKS

Table of n, a(n) for n=1..87.

EXAMPLE

The factorization f = (3*6*10) has prime factor choices (3,2,2), (3,3,2), (3,2,5), and (3,3,5), of which only (3,2,5) has all different parts, so f is counted under a(180).

The a(n) factorizations for n = 2, 12, 24, 36, 72, 120, 144, 180, 288:

(2) (2*6) (3*8) (4*9) (8*9) (3*5*8) (2*72) (4*5*9) (3*96)

(3*4) (4*6) (6*6) (2*36) (4*5*6) (3*48) (5*6*6) (4*72)

(2*12) (2*18) (3*24) (2*3*20) (4*36) (2*3*30) (6*48)

(3*12) (4*18) (2*5*12) (6*24) (2*5*18) (8*36)

(6*12) (2*6*10) (8*18) (2*6*15) (9*32)

(3*4*10) (9*16) (2*9*10) (12*24)

(12*12) (3*4*15) (16*18)

(3*5*12) (2*144)

(3*6*10)

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], Length[Union[Sort/@Select[Tuples[First /@ FactorInteger[#]&/@#], UnsameQ@@#&]]]==1&]], {n, 100}]

CROSSREFS

Multisets of this type are ranked by A368101, see also A368100, A355529.

For nonexistence we have A368413, complement A368414.

Subsets of this type are counted by A370584, see also A370582, A370583.

Maximal sets of this type are counted by A370585.

The version for partitions is A370594, see also A370592, A370593.

Subsets of this type are counted by A370638, see also A370636, A370637.

For unlabeled multiset partitions we have A370646, also A368098, A368097.

A001055 counts factorizations, strict A045778. 

A006530 gives greatest prime factor, least A020639.

A007716 counts non-isomorphic multiset partitions, connected A007718.

A027746 lists prime factors, A112798 indices, length A001222.

A058891 counts set-systems, unlabeled A000612, connected A323818.

A283877 counts non-isomorphic set-systems, connected A300913.

A355741 counts ways to choose a prime factor of each prime index.

For set-systems see A367902-A367908.

Cf. A000040, A000720, A003963, A340596, A340653, A355744, A355745, A368110.

Sequence in context: A371921 A327528 A264857 * A340596 A340654 A303837

Adjacent sequences: A370642 A370643 A370644 * A370646 A370647 A370648

KEYWORD

nonn

AUTHOR

Gus Wiseman, Mar 01 2024

STATUS

approved