login
The OEIS is supported by the many generous donors to the OEIS Foundation.

 

Logo
Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A317720 Numbers that are not uniform relatively prime tree numbers. 0
9, 12, 18, 20, 21, 23, 24, 25, 27, 28, 37, 39, 40, 44, 45, 46, 48, 49, 50, 52, 54, 56, 57, 60, 61, 63, 65, 68, 69, 71, 72, 73, 74, 75, 76, 80, 81, 83, 84, 87, 88, 89, 90, 91, 92, 96, 97, 98, 99, 103, 104, 107, 108, 111, 112, 115, 116, 117, 120, 121, 122, 124 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
COMMENTS
A positive integer n is a uniform relatively prime tree number iff either n = 1 or n is a prime number whose prime index is a uniform relatively prime tree number, or n is a power of a squarefree number whose prime indices are relatively prime and are themselves uniform relatively prime tree numbers. A prime index of n is a number m such that prime(m) divides n.
LINKS
EXAMPLE
The sequence of non-uniform tree numbers together with their Matula-Goebel trees begins:
9: ((o)(o))
12: (oo(o))
18: (o(o)(o))
20: (oo((o)))
21: ((o)(oo))
23: (((o)(o)))
24: (ooo(o))
25: (((o))((o)))
27: ((o)(o)(o))
28: (oo(oo))
37: ((oo(o)))
39: ((o)(o(o)))
40: (ooo((o)))
44: (oo(((o))))
45: ((o)(o)((o)))
MATHEMATICA
rupQ[n_]:=Or[n==1, If[PrimeQ[n], rupQ[PrimePi[n]], And[SameQ@@FactorInteger[n][[All, 2]], GCD@@PrimePi/@FactorInteger[n][[All, 1]]==1, And@@rupQ/@PrimePi/@FactorInteger[n][[All, 1]]]]];
Select[Range[200], !rupQ[#]&]
CROSSREFS
Sequence in context: A356842 A174525 A141552 * A162822 A087269 A153973
KEYWORD
nonn
AUTHOR
Gus Wiseman, Aug 05 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 | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 28 21:57 EDT 2024. Contains 371254 sequences. (Running on oeis4.)