This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A284991 #18 Apr 10 2017 15:18:16
%S A284991 1,0,0,0,0,0,0,0,0,0,0,0,0,0,1,1,0,10,20,45,44,265,1920,6300,13720,
%T A284991 20175,18000,7570,357435,2398900,7499940,14372820,18433415,15729000,
%U A284991 8171730,1975560,749649145,4695264000,13718863480,24545693760,29544855480,24545693760,13718863480,4695264000,749649145
%N A284991 Triangle T(n,t) read by rows: the number of n X n {0,1} matrices with trace t where each row sum and each column sum is 4.
%H A284991 Alois P. Heinz, <a href="/A284991/b284991.txt">Rows n = 0..10, flattened</a>
%H A284991 <a href="/index/Mat#binmat">Index entries for sequences related to binary matrices</a>
%e A284991 0: 1
%e A284991 1: 0 0
%e A284991 2: 0 0 0
%e A284991 3: 0 0 0 0
%e A284991 4: 0 0 0 0 1
%e A284991 5: 1 0 10 20 45 44
%e A284991 6: 265 1920 6300 13720 20175 18000 7570
%e A284991 7: 357435 2398900 7499940 14372820 18433415 15729000 8171730 1975560
%Y A284991 Cf. A058528 (row sums), A007105 (diagonal?), A139670 (symmetric matrices).
%K A284991 nonn,tabl
%O A284991 0,18
%A A284991 _R. J. Mathar_, Apr 07 2017
%E A284991 More terms from _Alois P. Heinz_, Apr 09 2017