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 A172806 #21 May 13 2019 02:10:28 %S A172806 1,1,5,120,10147,2224955,1047649905,936670590450,1455918295922650, %T A172806 3680232136895819610,14356628851597700179050, %U A172806 82857993930808028192521800,683327637694741065563262206250,7821620120684573354895941635688250 %N A172806 Number of n X n of nonnegative integers with all row and column sums equal to 4. %H A172806 R. H. Hardin, <a href="/A172806/b172806.txt">Table of n, a(n) for n = 0..56</a> %H A172806 Esther M. Banaian, <a href="http://digitalcommons.csbsju.edu/honors_thesis/24">Generalized Eulerian Numbers and Multiplex Juggling Sequences</a>, (2016). All College Thesis Program. Paper 24. %H A172806 M. L. Stein and P. R. Stein, <a href="http://dx.doi.org/10.2172/4180737">Enumeration of Linear Graphs and Connected Linear Graphs up to p = 18 Points</a>. Report LA-3775, Los Alamos Scientific Laboratory of the University of California, Los Alamos, NM, Oct 1967. %H A172806 M. L. Stein and P. R. Stein, <a href="/A001496/a001496.pdf">Enumeration of Stochastic Matrices with Integer Elements</a>, Report LA-4434, Los Alamos Scientific Laboratory of the University of California, Los Alamos, NM, Jun 1970. [Annotated scanned copy] %Y A172806 Cf. A000681, A001500, A172862, A172894, A172919, A172944, A172958. %Y A172806 Column k=4 of A257493. %K A172806 nonn %O A172806 0,3 %A A172806 _R. H. Hardin_, Feb 06 2010