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 A275517 #8 Aug 02 2016 07:15:13
%S A275517 1,0,0,4,39,472,7255,131876,2771685,66253552,1775801814,52761229240,
%T A275517 1721387545471,61187851111432,2353835271333611,97437447411025008,
%U A275517 4318780849687684325,204079128112017902848,10241833975586335217950,544031400274026445420368
%N A275517 Number of n-block bicoverings of an n-set.
%H A275517 Alois P. Heinz, <a href="/A275517/b275517.txt">Table of n, a(n) for n = 0..150</a>
%F A275517 a(n) = n! * [(x*y)^n] 1/exp(x+x^2/2*(exp(y)-1)) * Sum_{j>=0} x^j/j! * exp(C(j,2)*y).
%F A275517 a(n) = A059443(n,n).
%F A275517 a(n)/n! ~ c * d^n / n, where d = 2.942382880944169398..., c = 0.1111860502273875... . - _Vaclav Kotesovec_, Aug 02 2016
%e A275517 a(3) = 4: 1|123|23, 12|13|23, 12|123|3, 123|13|2.
%Y A275517 Main diagonal of A059443.
%K A275517 nonn
%O A275517 0,4
%A A275517 _Alois P. Heinz_, Jul 31 2016