login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A185894 Number of prime divisors (counted with multiplicity) of number of rings with n elements. 0
0, 0, 1, 1, 1, 1, 2, 1, 3, 1, 2, 1, 2, 1, 2, 2, 4, 1, 2, 2, 1, 2, 2, 2, 1, 4, 1, 2, 1, 2, 1, 3, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,7

COMMENTS

By convention, there is 1 ring with no elements. The first value that I don't know is a(32), where the number of rings with 32 elements was said by Christof Noebauer in 2000 to be >18590. The next value not known to me is a(64) =  where the same source gives the number of rings with 64 elements > 829826.  The articles by Christof Noebauer are linked to from A027623.

LINKS

Table of n, a(n) for n=0..32.

Eric W. Weisstein Ring

FORMULA

a(n) = A001222(A027623(n)).

EXAMPLE

a(16) = 4 because there are A027623(16) = 390 rings with 16 elements, and 390 = 2 * 3 * 5 * 13 has 4 prime divisors counted with multiplicity (in this example, each has multiplicity of 1).

CROSSREFS

Cf. A001222, A027623.

Sequence in context: A228098 A174532 A089242 * A214180 A184166 A029423

Adjacent sequences:  A185891 A185892 A185893 * A185895 A185896 A185897

KEYWORD

nonn,more,hard

AUTHOR

Jonathan Vos Post, Feb 05 2011

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified November 22 03:50 EST 2014. Contains 249803 sequences.