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!)
A316439 Irregular triangle where T(n,k) is the number of factorizations of n into k factors > 1, with k ranging from 1 to Omega(n). 2
1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 3, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 3, 1, 1, 1, 2, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 4, 3, 1, 1, 1, 1, 1, 1, 1, 3, 2, 1, 1, 1, 3 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,18

LINKS

Alois P. Heinz, Rows n = 1..20000, flattened

EXAMPLE

The factorizations of 24 are (2*2*2*3), (2*2*6), (2*3*4), (2*12), (3*8), (4*6), (24) so the 24th row is {1, 3, 2, 1}.

Triangle begins:

  {}

  1

  1

  1  1

  1

  1  1

  1

  1  1  1

  1  1

  1  1

  1

  1  2  1

  1

  1  1

  1  1

  1  2  1  1

  1

  1  2  1

  1

  1  2  1

  1  1

  1  1

  1

  1  3  2  1

  1  1

  1  1

  1  1  1

  1  2  1

  1

  1  3  1

MAPLE

g:= proc(n, k) option remember; `if`(n>k, 0, x)+

      `if`(isprime(n), 0, expand(x*add(`if`(d>k, 0,

      g(n/d, d)), d=numtheory[divisors](n) minus {1, n})))

    end:

T:= n-> `if`(n=1, [][], (p-> seq(coeff(p, x, i)

        , i=1..degree(p)))(g(n$2))):

seq(T(n), n=1..50);  # Alois P. Heinz, Aug 11 2019

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[#]==k&]], {n, 100}, {k, PrimeOmega[n]}]

CROSSREFS

Cf. A001222 (row lengths), A001055 (row sums), A001970, A007716, A045778, A162247, A259936, A281116, A303386.

Sequence in context: A295657 A163379 A006466 * A335078 A086597 A322320

Adjacent sequences:  A316436 A316437 A316438 * A316440 A316441 A316442

KEYWORD

nonn,tabf

AUTHOR

Gus Wiseman, Jul 03 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 September 23 16:17 EDT 2020. Contains 337314 sequences. (Running on oeis4.)