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A038018 Triangle: T(n,k), k<=n: groupoids with n elements and k idempotents.

%I A038018 #15 Feb 02 2023 15:25:52
%S A038018 1,0,1,3,4,3,978,1485,729,138,56630832,75503872,37755904,8390656,
%T A038018 700688,813802235250650,1017252851596875
%N A038018 Triangle: T(n,k), k<=n: groupoids with n elements and k idempotents.
%H A038018 <a href="/index/Gre#groupoids">Index entries for sequences related to groupoids</a>
%e A038018 Triangle begins:
%e A038018          1;
%e A038018          0,        1;
%e A038018          3,        4,        3;
%e A038018        978,     1485,      729,     138;
%e A038018   56630832, 75503872, 37755904, 8390656, 700688;
%e A038018   ...
%Y A038018 Row sums are A001329.
%Y A038018 Main diagonal is A030247.
%Y A038018 Columns k=0..1 are A030250, A030253.
%K A038018 nonn,tabl,more
%O A038018 0,4
%A A038018 _Christian G. Bower_, May 15 1998