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 A174638 #7 Oct 29 2024 20:36:56
%S A174638 0,0,0,0,0,1350,529200,172872000,58352555520,21677788944000,
%T A174638 9059008787136000,4286753834515891200,2297335836334687948800,
%U A174638 1390520517156693315993600,946759961227258909995264000
%N A174638 Number of n X n (0,1)-matrices with two 1's in each row and permanent equal to 8.
%C A174638 If a (0,1)-matrix with two 1's in each row has positive permanent, then it equals to a power of 2.
%D A174638 J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1967, Ch.4, 66-79.
%D A174638 V. S. Shevelev, On the permanent of the stochastic (0,1)-matrices with equal row sums, Izvestia Vuzov of the North-Caucasus region, Nature sciences 1 (1997), 21-38 (in Russian)
%F A174638 For m >= 1, the number of n X n (0,1)-matrices with two 1's in each row with the permanent 2^m is n! * n^(n-1) / 2^m * Sum{k=2,...,n} k * n^(-k) * binomial(n,k) * d(k,m), where d(k,m) are associated Stirling numbers of the first kind (see Riordan, p. 75).
%Y A174638 Cf. A000276, A001866, A174637, A174586.
%K A174638 nonn
%O A174638 1,6
%A A174638 _Vladimir Shevelev_, Mar 25 2010