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 A059089 Number of labeled T_0-hypergraphs with n distinct hyperedges (empty hyperedge excluded). 7
 2, 3, 27, 18209, 2369751602470, 5960531437867327674538684858601298, 479047836152505670895481842190009123676957243077039687942939196956404642582185242435050 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS A hypergraph is a T_0 hypergraph if for every two distinct nodes there exists a hyperedge containing one but not the other node. LINKS FORMULA Column sums of A059087. a(n) = Sum_{k = 0..n} (-1)^(n-k)*A059086(k); a(n) = (1/n!)*Sum_{k = 0..n+1} stirling1(n+1, k)*floor(( 2^(k-1))!*exp(1)). EXAMPLE a(2)=27; There are 27 labeled T_0-hypergraphs with 2 distinct hyperedges (empty hyperedge excluded): 3 2-node hypergraphs, 12 3-node hypergraphs and 12 4-node hypergraphs. a(3) = (1/3!)*(-6*[1!*e]+11*[2!*e]-6*[4!*e]+[8!*e]) = (1/3!)*(-6*2+11*5-6*65+109601) = 18209, where [k!*e] := floor(k!*exp(1)). MAPLE with(combinat): Digits := 1000: for n from 0 to 8 do printf(`%d, `, (1/n!)*sum(stirling1(n+1, k)*floor((2^(k-1))!*exp(1)), k=0..n+1)) od: CROSSREFS Cf. A059084-A059088. Sequence in context: A126655 A242520 A132533 * A098812 A073049 A349826 Adjacent sequences:  A059086 A059087 A059088 * A059090 A059091 A059092 KEYWORD easy,nonn AUTHOR Goran Kilibarda, Vladeta Jovovic, Dec 27 2000 EXTENSIONS More terms from James A. Sellers, Jan 24 2001 STATUS approved

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Last modified October 7 16:02 EDT 2022. Contains 357275 sequences. (Running on oeis4.)