

A037291


Number of rings with 1 containing n elements.


9



1, 1, 1, 4, 1, 1, 1, 11, 4, 1, 1, 4, 1, 1, 1, 50, 1, 4, 1, 4, 1, 1, 1, 11, 4, 1, 12, 4, 1, 1, 1, 208, 1, 1, 1, 16, 1, 1, 1, 11, 1, 1, 1, 4, 4, 1, 1, 50, 4, 4, 1, 4, 1, 11, 1, 11, 1, 1, 1, 4, 1, 1, 4
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OFFSET

1,4


COMMENTS

Many authors simply call these "rings". They are also known as unital rings, rings with unity, or rings with identity.  Charles R Greathouse IV, Aug 12 2015
Is this sequence multiplicative? That is, if p and q are distinct primes, is it true that a(p^i*q^j) = a(p^i)*a(q^j)?  Jianing Song, Oct 26 2019. The answer is yes  see the Eric M. Rains link.  N. J. A. Sloane, Oct 27 2019


LINKS

Table of n, a(n) for n=1..63.
C. Noebauer, Home page [Archived copy as of 2008 from web.archive.org]
Eric M. Rains, The number of unital rings with n elements is a multiplicative function of n.


CROSSREFS

Cf. A027623, A037221.
Sequence in context: A184729 A127707 A113196 * A222317 A063851 A124777
Adjacent sequences: A037288 A037289 A037290 * A037292 A037293 A037294


KEYWORD

nonn,nice,hard,mult


AUTHOR

Christian G. Bower, Jun 15 1998


EXTENSIONS

a(16) and a(32)a(63) from Christof Noebauer (christof.noebauer(AT)algebra.unilinz.ac.at), Sep 29 2000
Keyword 'mult' added by Jianing Song, Feb 02 2020


STATUS

approved



