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!)
A304817 Number of divisors of n that are either 1 or not a perfect power. 7
1, 2, 2, 2, 2, 4, 2, 2, 2, 4, 2, 5, 2, 4, 4, 2, 2, 5, 2, 5, 4, 4, 2, 6, 2, 4, 2, 5, 2, 8, 2, 2, 4, 4, 4, 6, 2, 4, 4, 6, 2, 8, 2, 5, 5, 4, 2, 7, 2, 5, 4, 5, 2, 6, 4, 6, 4, 4, 2, 11, 2, 4, 5, 2, 4, 8, 2, 5, 4, 8, 2, 8, 2, 4, 5, 5, 4, 8, 2, 7, 2, 4, 2, 11, 4, 4 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

First differs from A183095 at a(80) = 8, A183095(80) = 7.

LINKS

Table of n, a(n) for n=1..86.

FORMULA

a(n) = A183096(n) + 1.

EXAMPLE

The a(72) = 8 divisors of 72 that are either 1 or not a perfect power are {1, 2, 3, 6, 12, 18, 24, 72}. Missing are {4, 8, 9, 36}.

MATHEMATICA

Table[DivisorSum[n, Boole[GCD@@FactorInteger[#][[All, 2]]==1]&], {n, 100}]

PROG

(PARI) a(n) = sumdiv(n, d, !ispower(d)); \\ Michel Marcus, May 19 2018

CROSSREFS

Cf. A000005, A001597, A007916, A091050, A183096, A304326, A304362, A304653, A304779, A304819, A304820.

Sequence in context: A073180 A316398 A183095 * A242802 A277561 A317684

Adjacent sequences:  A304814 A304815 A304816 * A304818 A304819 A304820

KEYWORD

nonn

AUTHOR

Gus Wiseman, May 18 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 June 21 09:45 EDT 2021. Contains 345358 sequences. (Running on oeis4.)