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 A247417 #46 May 24 2018 15:54:56 %S A247417 1,3,11,35,132,471,1806,7042,28494,118662,510517,2262738,10337474, %T A247417 48625631,235357470,1171163995,5986424739,31403695142,168913667164, %U A247417 930739116386,5249162406890,30275048671498,178428441191289,1073737691984694,6592909590432719 %N A247417 Number of nonisomorphic binary n X n matrices with two 1's per column under row and column permutations. %H A247417 Andrew Howroyd, <a href="/A247417/b247417.txt">Table of n, a(n) for n = 2..50</a> %H A247417 Marko Riedel, <a href="/A247417/a247417.maple.txt">MAPLE Cycle Indices and Burnside Computation for Non-Isomorphic N by N binary matrices with K entries per column under row and column permutation</a> %H A247417 StackExchange, <a href="http://math.stackexchange.com/questions/616834/">How many arrays with crossed cells, order of rows/columns irrelevant</a>, Dec 13 2013 %p A247417 Using the uploaded program the call is seq(matrix_marks(n,2), n=3..15); %o A247417 (PARI) \\ See A304942 for Blocks %o A247417 a(n) = Blocks(n, n, 2); \\ _Andrew Howroyd_, May 24 2018 %Y A247417 Column k=2 of A304942. %Y A247417 Cf. A247596, A247597, A247598. %K A247417 nonn %O A247417 2,2 %A A247417 _Marko Riedel_, Sep 21 2014 %E A247417 Terms a(17) and beyond from _Andrew Howroyd_, May 23 2018