A072447 - OEIS

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A072447

Number of subsets S of the power set P{1,2,...,n} such that: {1}, {2},..., {n} are all elements of S; {1,2,...n} is an element of S; if X and Y are elements of S and X and Y have a non-empty intersection, then the union of X and Y is an element of S.

1, 1, 8, 378, 252000, 17197930224 (list; graph; refs; listen; history; internal format)

	OFFSET	`1,3`
	LINKS	`Wim van Dam, Sub Power Set Sequences`
	EXAMPLE	`a(3)=8 because of the 8 sets: {{1}, {2}, {3}, {1, 2, 3}}; {{1}, {2}, {3}, {1, 2}, {1, 2, 3}}; {{1}, {2}, {3}, {1, 3}, {1, 2, 3}}; {{1}, {2}, {3}, {2, 3}, {1, 2, 3}}; {{1}, {2}, {3}, {1, 2}, {1, 3}, {1, 2, 3}}; {{1}, {2}, {3}, {1, 2}, {2, 3}, {1, 2, 3}}; {{1}, {2}, {3}, {1, 3}, {2, 3}, {1, 2, 3}}; {{1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}}.`
	CROSSREFS	`Cf. A072444, A072445, A072446.` `Sequence in context: A193187 A038016 A206690 * A151932 A096205 A162445` `Adjacent sequences: A072444 A072445 A072446 * A072448 A072449 A072450`
	KEYWORD	`nonn`
	AUTHOR	`Wim van Dam (vandam(AT)cs.berkeley.edu), Jun 18 2002`

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Last modified February 12 15:29 EST 2012. Contains 205429 sequences.