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A296241 Finite number of units in a commutative ring; nonnegative even numbers together with products of Mersenne numbers. 2
0, 1, 2, 3, 4, 6, 7, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 26, 27, 28, 30, 31, 32, 34, 36, 38, 40, 42, 44, 45, 46, 48, 49, 50, 52, 54, 56, 58, 60, 62, 63, 64, 66, 68, 70, 72, 74, 76, 78, 80, 81, 82, 84, 86, 88, 90, 92, 93, 94, 96, 98, 100, 102, 104, 105, 106, 108, 110, 112, 114, 116, 118, 120, 122, 124, 126 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Zero together with orders of finite abelian groups that appear as the group of units in a commutative ring (Chebolu and Lockridge).

Equals A005843 union A282572.

LINKS

Table of n, a(n) for n=1..78.

S. Chebolu and K. Lockridge, How Many Units Can a Commutative Ring Have?, Amer. Math. Monthly, 124 (2017), 960-965; arXiv, arXiv:1701.02341 [math.AC], 2017.

EXAMPLE

The even integers {0, +-2, +-4, ...} form a commutative ring with no (multiplicative) units, so a(1) = 0.

CROSSREFS

Cf. A005843, A282572.

A070932 is closely related.

Sequence in context: A141825 A238369 A296858 * A070932 A161577 A093686

Adjacent sequences:  A296238 A296239 A296240 * A296242 A296243 A296244

KEYWORD

nonn

AUTHOR

Jonathan Sondow, Dec 14 2017

STATUS

approved

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Last modified November 19 22:34 EST 2019. Contains 329323 sequences. (Running on oeis4.)