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!)
A091443 Multiperfect numbers n which are divisible by sopfr(n) (multiperfect number: sigma(n) = k*n with k integer, sopfr: Sum of prime factors with repetition). 4
1379454720, 14182439040, 212517062615531520, 27099073228001299660800, 680489641226538823680000, 15229814702070563916152832000, 34111227434420791224041472000, 59023729003862626557345792000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The sequence contains multiperfect numbers with multiplicity k from 3..8. They are extracted from a list with about 5000 multiperfect numbers with multiplicity from 2..11. Because of the size of these numbers, no numbers with multiplicity k > 8 were found, even though there were about 3000 of them in the list. 95% of the multiperfect numbers with multiplicity from 3..8 are known.

Conjecture: the sequence is finite.

There are 5255 multiperfect numbers known with multiplicity 3 to 11. No more findings for A091443 so we still have 33 multiperfect numbers divisible by their sopfr (without the trivial case 1). With multiplicity 3..8 quite surely all are found (only very few - if any - missing). It is estimated that there are about 2200 with multiplicity 9 and 2091 of them are already found. With multiplicity 10 of estimated 4500 1161 are known. So far no multiperfect number with multiplicity 9 or 10 is divisible by its sopfr (with repetition). Using sopfr without repetition (A114887), there is one number with multiplicity 9 (or more). - Sven Simon, Feb 12 2012

LINKS

Sven Simon, Table of n, a(n) for n = 1..33 [Conjectured to be complete]

Achim Flammenkamp, The Multiply Perfect Numbers Page (See here for the latest information about the search)

Achim Flammenkamp, he Multiply Perfect Numbers Page [Local copy in pdf format of the page as of Jun 04 2020, made with permission of the author]

Achim Flammenkamp, Datafile_2013_12_31 (with 5311 multiperfect numbers). [Sven Simon, Feb 15 2014]

Eric Weisstein's World of Mathematics, Multiperfect numbers

EXAMPLE

a(1): 1379454720 = 2^8*3*5*7*19*37*73, sopfr(n)= 2^5*5.

CROSSREFS

Cf. A000203, A001414, A005820, A027687, A046060, A046061.

Intersection of A007691 and A036844. - Michel Marcus, Oct 08 2017

Sequence in context: A343078 A345010 A338516 * A114888 A347114 A105015

Adjacent sequences:  A091440 A091441 A091442 * A091444 A091445 A091446

KEYWORD

nonn

AUTHOR

Sven Simon, Jan 10 2004

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 January 28 15:20 EST 2022. Contains 350657 sequences. (Running on oeis4.)