id:A030449 - OEIS Search Results

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Number of elements in the free band (idempotent semigroup) on n generators.

+0
3

1, 6, 159, 332380, 2751884514765, 272622932796281408879065986, 3641839910835401567626683593436003894250931310990279691 (list; graph; listen)

	OFFSET	`1,2`
	COMMENT	`An idempotent semigroup satisfies the equation xx=x for any element x.`
	REFERENCES	`J. Howie, Fundamentals of Semigroup Theory, Oxford University Press 1995, p. 123.`
	LINKS	`Index entries for sequences related to semigroups`
	FORMULA	`a_n=\Sum_{k=1}^{n} C(n, k) A030450(k).`
	CROSSREFS	`Cf. A030450. A005345(n)=a(n)+1.` `Sequence in context: A003460 A157626 A128120 this_sequence A120277 A015086 A052466` `Adjacent sequences: A030446 A030447 A030448 this_sequence A030450 A030451 A030452`
	KEYWORD	`nonn`
	AUTHOR	`marcel_j(AT)hilbert.maths.utas.edu.au (Marcel Jackson)`

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Last modified December 4 23:11 EST 2009. Contains 170347 sequences.