A350876 - OEIS

A350876

a(n) is the number of nonisomorphic flexible left-right-alternative magmas with n elements. That is, a(n) is the number of nonisomorphic magmas with n elements which satisfy all of the identities x(yx) = (xy)x, (xx)y = x(xy), and x(yy) = (xy)y (for all x and y).

1, 1, 5, 33, 675, 65066, 41160471

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OFFSET

0,3

COMMENTS

Compare A350873 and A350875, which are the numbers of flexible magmas with n elements and left-right-alternative magmas with n elements (up to isomorphism). The fact that a(n) < A350875(n) for n >= 3 means that left-right-alternativity for magmas (the identities (xx)y = x(xy) and x(yy) = (xy)y) does not imply flexibility (x(yx) = (xy)x). This is in contrast to the situation for non-associative rings, where this implication does hold (due to the additional additive structure).

LINKS

Table of n, a(n) for n=0..6.

EXAMPLE

There are 10 nonisomorphic magmas with 2 elements, 5 of which are flexible and left-right-alternative, so a(2) = 5.

Similarly there are 3330 nonisomorphic magmas with 3 elements, 33 of which satisfy all of (xy)x = x(yx), (xx)y = x(xy), and x(yy) = (xy)y for all x and y, so a(3) = 33.

CROSSREFS

Cf. A001329 (magmas), A350873 (flexible magmas), A350874 (left/right-alternative magmas), A350875 (left-right-alternative magmas).

Sequence in context: A134152 A140424 A295090 * A268296 A212296 A276160

Adjacent sequences: A350873 A350874 A350875 * A350877 A350878 A350879

KEYWORD

nonn,hard,more

AUTHOR

Joel Brennan, Jan 23 2022

EXTENSIONS

a(5)-a(6) from Andrew Howroyd, Jan 25 2022

STATUS

approved