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Triangle: T(n,k), k<=n: groupoids with n elements and k idempotents.
3

%I #15 Feb 02 2023 15:25:52

%S 1,0,1,3,4,3,978,1485,729,138,56630832,75503872,37755904,8390656,

%T 700688,813802235250650,1017252851596875

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

%H <a href="/index/Gre#groupoids">Index entries for sequences related to groupoids</a>

%e Triangle begins:

%e 1;

%e 0, 1;

%e 3, 4, 3;

%e 978, 1485, 729, 138;

%e 56630832, 75503872, 37755904, 8390656, 700688;

%e ...

%Y Row sums are A001329.

%Y Main diagonal is A030247.

%Y Columns k=0..1 are A030250, A030253.

%K nonn,tabl,more

%O 0,4

%A _Christian G. Bower_, May 15 1998