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 A006326 Total preorders. (Formerly M3931) 1
 1, 5, 24, 122, 680, 4155, 27776, 202084, 1592064, 13513825, 123025408, 1196165886, 12374422528, 135740585015, 1573990072320, 19239037403528, 247255523459072, 3333340694137725, 47039231504678912, 693488743931379010, 10661950808321949696, 170659875799127955955 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,2 REFERENCES N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Table of n, a(n) for n=3..24. G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30. G. Kreweras, Les préordres totaux compatibles avec un ordre partiel, Math. Sci. Humaines No. 53 (1976), 5-30. (Annotated scanned copy) MAPLE # After Alois P. Heinz in A000111: b := proc(u, o) option remember; `if`(u + o = 0, 1, add(b(o - 1 + j, u - j), j = 1..u)) end: a := n -> (n-2)*b(n-1, 1)/2: seq(a(n), n = 3..23); # Peter Luschny, Oct 27 2017 MATHEMATICA b[u_, o_] := b[u, o] = If[u+o == 0, 1, Sum[b[o-1+j, u-j], {j, 1, u}]]; a[n_] := (n-2) b[n-1, 1]/2; Array[a, 22, 3] (* Jean-François Alcover, Jun 01 2019, from Maple *) CROSSREFS Cf. A000111, A079502. Sequence in context: A255715 A163610 A055825 * A058120 A271544 A275267 Adjacent sequences: A006323 A006324 A006325 * A006327 A006328 A006329 KEYWORD nonn AUTHOR N. J. A. Sloane EXTENSIONS More terms from Sean A. Irvine, Mar 12 2017 STATUS approved

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Last modified September 12 05:07 EDT 2024. Contains 375842 sequences. (Running on oeis4.)