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%I #4 Sep 15 2022 07:59:52
%S 1,1,6,71,1433,44443,1968580,118159971,9240555677,913352224942,
%T 111374887418013,16428282185046946,2883740893056526715,
%U 594152447495864629867,142006380268368661423424,38973735372090120549251580,12174162204364698538764222978,4294569227671480526607187583713
%N Number of n X n triangular matrices with nonnegative integer entries and without zero rows or columns such that sum of all entries is equal to 2n.
%F a(n) = A137251(2n,n).
%Y Cf. A137251.
%K nonn
%O 0,3
%A _Alois P. Heinz_, Sep 14 2022
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