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%I #3 Mar 30 2012 18:52:19
%S 0,1,5,203,115975,1382958545,474869816156751,6160539404599934652455,
%T 3819714729894818339975525681317,
%U 139258505266263669602347053993654079693415
%N Number of set partitions of n(n-1)/2.
%C Among n persons we have (n^2-n)/2 undirected relations. We can set partition these relations into (up to) A137736(n)=Bell((n^2-n)/2) sets.
%C The number of graphs on n labeled nodes is A006125(n)=sum(binomial((n^2-n)/2,k),k=0..(n^2-n)/2).
%C The number of set partitions of n(n-1)/2 is A137736(n)=sum(Stirling2((n^2-n)/2,k),k=0..(n^2-n)/2).
%C See also A066655 which equals A066555(n)=sum(P((n^2-n)/2,k),k=0..(n^2-n)/2) where P(n) is the number of integer partitions of n.
%C See also A135084 = A000110(2^n-1) and A135085 = A000110(2^n).
%F a(n) = Bell(n(n-1)/2) = A000110(n(n-1)/2)
%e a(4) = Bell(6) = 203.
%p for n from 1 to 10 do a(n):=bell((n^2-n)/2): print(a(n)); od:
%Y Cf. A006125, A066655, A135084, A135085.
%K nonn
%O 1,3
%A _Thomas Wieder_, Feb 09 2008
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