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 A176901 #39 Aug 08 2020 05:25:52
%S A176901 4,72,1584,70720,3948480,284570496,25574768128,2808243910656,
%T A176901 369925183388160,57585548812887040,10458478438093154304,
%U A176901 2191805683821733404672,525011528578874444283904,142540766765931981615759360,43542026550306796238178877440,14867182204795857282384287236096,5640920219495105293649671985430528
%N A176901 Number of 3 X n semireduced Latin rectangles, that is, having exactly n fixed points in the first two rows.
%C A176901 A Latin rectangle is called reduced if its first row is [1,2,...,n] (the number of 3 X n reduced Latin rectangles is given in A000186). Therefore a Latin rectangle having exactly n fixed points in the first two rows may be called "semireduced". Thus if A1(i), A2(i), i=1,...,n, are the first two rows, then, for every i, either A1(i)=i or A2(i)=i.
%H A176901 V. S. Shevelev, <a href="http://mi.mathnet.ru/eng/dm720">Reduced Latin rectangles and square matrices with equal row and column sums</a>, Diskr. Mat.(J. of the Akademy of Sciences of Russia) 4(1992), 91-110.
%H A176901 V. S. Shevelev, <a href="http://mi.mathnet.ru/eng/dm665">Modern enumeration theory of permutations with restricted positions</a>, Diskr. Mat., 1993, 5, no.1, 3-35 (Russian).
%H A176901 V. S. Shevelev, <a href="http://dx.doi.org/10.1515/dma.1993.3.3.229">Modern enumeration theory of permutations with restricted positions</a>, English translation, Discrete Math. and Appl., 1993, 3:3, 229-263 (pp. 255-257).
%F A176901 Let F_n = A087981(n) = n! * Sum_{2*k_2+...+n*k_n=n, k_i>=0} Product_{i=2..n} 2^k_i/(k_i!*i^k_i). Then a(n) = Sum_{k=0..floor(n/2)} binomial(n,k) * F_k * F_(n-k) * u_(n-2*k), where u(n) = A000179(n). - _Vladimir Shevelev_, Mar 30 2016
%Y A176901 Cf. A174563, A000179, A000186, A087981, A094047, A174556, A174560, A174561.
%K A176901 nonn
%O A176901 3,1
%A A176901 _Vladimir Shevelev_, Apr 28 2010
%E A176901 More terms from _William P. Orrick_, Jul 25 2020