login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A317144 Number of refinement-ordered pairs of factorizations of n into factors > 1. 24
1, 1, 1, 3, 1, 3, 1, 6, 3, 3, 1, 9, 1, 3, 3, 14, 1, 9, 1, 9, 3, 3, 1, 23, 3, 3, 6, 9, 1, 12, 1, 26, 3, 3, 3, 31, 1, 3, 3, 23, 1, 12, 1, 9, 9, 3, 1, 56, 3, 9, 3, 9, 1, 23, 3, 23, 3, 3, 1, 41, 1, 3, 9, 55, 3, 12, 1, 9, 3, 12, 1, 82, 1, 3, 9, 9, 3, 12, 1, 56, 14 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

If x and y are factorizations of the same integer and it is possible to produce x by further factoring the factors of y, flattening, and sorting, then x <= y.

As this is a sequence computed from exponents in factorization of n, distinct values of a(n) in this sequence can be found by computing a(A025487(k)) for k >= 0. - David A. Corneth, Jul 30 2018

LINKS

Table of n, a(n) for n=1..81.

Gus Wiseman, The poset of factorizations of 36, ordered by refinement.

Index entries for sequences computed from exponents in factorization of n

FORMULA

a(n) >= A001055(n) + floor(A000005(n) / 2) - 1. - David A. Corneth, Jul 30 2018

EXAMPLE

The a(12) = 9 ordered pairs:

  (2*2*3) <= (12)

  (2*2*3) <= (2*6)

  (2*2*3) <= (3*4)

  (2*2*3) <= (2*2*3)

    (2*6) <= (12)

    (2*6) <= (2*6)

    (3*4) <= (12)

    (3*4) <= (3*4)

     (12) <= (12)

MATHEMATICA

sps[{}]:={{}}; sps[set:{i_, ___}]:=Join@@Function[s, Prepend[#, s]&/@sps[Complement[set, s]]]/@Cases[Subsets[set], {i, ___}];

mps[set_]:=Union[Sort[Sort/@(#/.x_Integer:>set[[x]])]&/@sps[Range[Length[set]]]];

facs[n_]:=If[n<=1, {{}}, Join@@Table[Map[Prepend[#, d]&, Select[facs[n/d], Min@@#>=d&]], {d, Rest[Divisors[n]]}]];

faccaps[fac_]:=Union[Sort/@Apply[Times, mps[fac], {2}]];

Table[Sum[Length[faccaps[fac]], {fac, facs[n]}], {n, 100}]

CROSSREFS

Cf. A000005, A001055, A007716, A025487, A045778, A162247, A281113, A317142, A317145, A317146.

Sequence in context: A236800 A126212 A066637 * A050336 A281113 A236757

Adjacent sequences:  A317141 A317142 A317143 * A317145 A317146 A317147

KEYWORD

nonn

AUTHOR

Gus Wiseman, Jul 22 2018

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified July 9 05:53 EDT 2020. Contains 335538 sequences. (Running on oeis4.)