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!)
A327054 a(n) is the smallest number m such that the antiharmonic mean of the divisors is n, or 0 if no such m exists. 0
1, 0, 4, 0, 0, 0, 9, 0, 0, 0, 16, 0, 20, 0, 0, 0, 0, 0, 0, 0, 25, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 50, 0, 0, 0, 0, 0, 0, 0, 49, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 81, 0, 100, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 144, 0, 0, 0, 0, 0, 0, 0 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

a(n) = the smallest number m such that sigma_2(n) / sigma_1(n) = A001157(m) / A000203(m) = n, or 0 if no such m exists.

Zeros occur if n is not in A176799.

See A000290, A091911 and A162538 for like sequences for geometric, arithmetic and harmonic means of the divisors.

LINKS

Table of n, a(n) for n=1..84.

EXAMPLE

a(3) = 4 because 4 is the smallest number m with sigma_2(m) / sigma_1(m) = 3; sigma_2(4) / sigma_1(4) = 21 / 7 = 3.

PROG

(MAGMA) A372054:=func<n|exists(r){m:m in[1..10000] |  IsIntegral(&+[d^2: d in Divisors(m)] / SumOfDivisors(m)) and (&+[d^2: d in Divisors(m)] / SumOfDivisors(m)) eq n}select r else 0>; [A372054(n): n in[1..100]]

CROSSREFS

Cf. A020487, A176797, A176799, A176800.

Sequence in context: A003194 A286875 A105570 * A101419 A060278 A046770

Adjacent sequences:  A327051 A327052 A327053 * A327055 A327056 A327057

KEYWORD

nonn

AUTHOR

Jaroslav Krizek, Oct 06 2019

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 5 18:48 EDT 2020. Contains 334854 sequences. (Running on oeis4.)