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!)
A322075 Number of factorizations of n into nonprime squarefree numbers > 1. 1
1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 1, 1, 0, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,210

COMMENTS

First term greater than 1 is a(210) = 4.

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..10000

EXAMPLE

The a(420) = 3 factorizations: (6*70), (10*42), (14*30).

MATHEMATICA

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

Table[Length[sqnopfacs[n]], {n, 100}]

CROSSREFS

Cf. A000469, A001055, A001221, A001222, A005117, A007716, A318871, A318953, A320655, A320656, A320658, A320659.

Sequence in context: A079998 A339661 A320656 * A288220 A173856 A288926

Adjacent sequences:  A322072 A322073 A322074 * A322076 A322077 A322078

KEYWORD

nonn

AUTHOR

Gus Wiseman, Nov 25 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 25 03:53 EDT 2021. Contains 346283 sequences. (Running on oeis4.)