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 A110058 #28 Apr 18 2020 22:22:59 %S A110058 1,1,3,55,10147,22069251,602351808741,215717608046511873, %T A110058 1046591482728407939338275,70417932475495769964322670258947, %U A110058 66880713903767740581650957184096513655153,909176713758393122455793478657031533216492953328933,178876969166665269546249744608783223036842010760723370462856181,514016665650183402309555825250370336139392333285719205357202846243695510965 %N A110058 Number of nonnegative integer matrices of order n for which all row and column sums equal n. %C A110058 Computed by a method that involves summing a multivariate generating function over roots of unity. %H A110058 E. R. Canfield, B. D. McKay, <a href="http://dx.doi.org/10.1007/s00493-010-2426-1">Asymptotic enumeration of integer matrices with large equal row and column sums</a>, Combinatorica 30 (6) (2010) 655-680 %F A110058 log a(n) = 2(log 2)*n^2 - n*(log n) - n*(log 4*Pi) + (log n) + O(1). - _Igor Pak_, May 15 2019 %e A110058 a(2) = 3 due to the matrices [1,1 | 1,1], [0,2 | 2,0] and [2,0 | 0,2]. %o A110058 (Sage) %o A110058 from sage.combinat.integer_matrices import IntegerMatrices %o A110058 [IntegerMatrices([n]*n, [n]*n).cardinality() for n in (0..6)] # _Freddy Barrera_, Dec 27 2018 %Y A110058 Cf. A058407, A058410, A058391. %Y A110058 Main diagonal of A257493 and A333901. %K A110058 nonn %O A110058 0,3 %A A110058 _Brendan McKay_, Sep 04 2005 %E A110058 a(0)=1 prepended by _Alois P. Heinz_, Apr 26 2015