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A037289 Number of commutative rings with n elements. 5
1, 2, 2, 9, 2, 4, 2, 34, 9, 4, 2, 18, 2, 4, 4, 162, 2, 18, 2, 18, 4, 4, 2, 68, 9, 4, 36, 18, 2, 8, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

These rings do not necessarily contain an identity element.

This sequence is multiplicative. See the reference "The Numbers of Small Rings" below, which proves the result for all rings; restricting to commutative rings only makes the proof easier. - Conjecture by Mitch Harris, Apr 19 2005, proof found by Franklin T. Adams-Watters, Jul 10 2012

LINKS

Table of n, a(n) for n=1..31.

A. V. Lelechenko, Parity of the number of primes in a given interval and algorithms of the sublinear summation, arXiv preprint arXiv:1305.1639, 2013

C. Noebauer, Home page [Archived copy as of 2008 from web.archive.org]

Christof Noebauer, The numbers of small rings (PostScript).

C. Noebauer, Thesis on the enumeration of near-rings

Bjorn Poonen, The moduli space of commutative algebras of finite rank, J. Eur. Math. Soc. (JEMS) 10:3 (2008), pp. 817-836. arXiv:0608491

FORMULA

a(p^n) = p^(2/27 * n^3 + O(n^(8/3))), see Theorems 11.2 and 11.3 in Poonen 2008. - Charles R Greathouse IV, Jul 10 2012

CROSSREFS

Cf. A027623, A037291.

Sequence in context: A199058 A082838 A074961 * A037290 A155936 A167594

Adjacent sequences:  A037286 A037287 A037288 * A037290 A037291 A037292

KEYWORD

nonn,nice,more,hard,mult

AUTHOR

Christian G. Bower, Jun 15 1998.

EXTENSIONS

a(16) from Christof Noebauer (christof.noebauer(AT)algebra.uni-linz.ac.at), Sep 29, 2000, who reports that the sequence continues a(32) = ? (> 876), a(33) = 4, 4, 4, 81, 2, 4, 4, 68, 2, 8, 2, 18, 18, 4, 2, 324, 9, 18, 4, 18, 2, 72, 4, 68, 4, 4, 2, 36, 2, 4, 18 = a(63), a(64) = ? (> 12696)

STATUS

approved

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Last modified July 25 02:45 EDT 2014. Contains 244897 sequences.