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%I M4920 #26 Jun 22 2017 10:39:38
%S 1,1,13,4683,102247563,230283190977853,81124824998504073881821,
%T 6297562064950066033518373935334635,
%U 144199280951655469628360978109406917583513090155
%N Number of dissimilarity relations on an n-set.
%D M. Schader, Hierarchical analysis: classification with ordinal object dissimilarities, Metrika, 27 (1980), 127-132.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H Vincenzo Librandi, <a href="/A006541/b006541.txt">Table of n, a(n) for n = 1..29</a>
%H M. Schader, <a href="/A005121/a005121_1.pdf">Hierarchical analysis: classification with ordinal object dissimilarities</a>, Metrika, 27 (1980), 127-132. [Annotated scanned copy]
%H M. Schader, <a href="/A005121/a005121.pdf">Letter to N. J. A. Sloane</a>, Aug 25 1981.
%F Sum_{i=0..m-1} (m-i)!*Stirling2(m, m-i), where m = n(n-1)/2.
%t a[n_] := PolyLog[-n(n-1)/2, 1/2]/2; a[1]=1; Table[a[n], {n, 1, 9}] (* _Jean-François Alcover_, Jun 28 2012, after _Wouter Meeussen_ *)
%o (PARI) a(n)=ceil(polylog(-n*(n-1)/2, 1/2)/2) \\ _Charles R Greathouse IV_, Aug 27 2014
%Y Cf. A005121.
%Y A000670(n(n-1)/2).
%K nonn,nice,easy
%O 1,3
%A _N. J. A. Sloane_
%E More terms from _James A. Sellers_, Jan 19 2000
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