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 A060090 #11 Jan 30 2020 14:23:45
%S A060090 1,0,3,23,290,4298,79143,1702923,42299820,1188147639,37276597020,
%T A060090 1291633545897,48995506718702,2019395409175529,89864601931874318,
%U A060090 4294295828157319651,219321170795303112118,11922219151375200468886
%N A060090 Number of ordered bicoverings of an unlabeled n-set.
%H A060090 Andrew Howroyd, <a href="/A060090/b060090.txt">Table of n, a(n) for n = 0..200</a>
%F A060090 E.g.f. for ordered k-block bicoverings of an unlabeled n-set is exp(-x-x^2/2*y/(1-y)) * Sum_{k>=0} 1/(1-y)^binomial(k,2)*x^k/k!.
%e A060090 There are 23 ordered bicoverings of an unlabeled 3-set, 7 3-block bicoverings:
%e A060090 1 ( { 3 }, { 1, 2 }, { 1, 2, 3 } )
%e A060090 2 ( { 3 }, { 1, 2, 3 }, { 1, 2 } )
%e A060090 3 ( { 2, 3 }, { 1 }, { 1, 2, 3 } )
%e A060090 4 ( { 2, 3 }, { 1, 3 }, { 1, 2 } )
%e A060090 5 ( { 2, 3 }, { 1, 2, 3 }, { 1 } )
%e A060090 6 ( { 1, 2, 3 }, { 3 }, { 1, 2 } )
%e A060090 7 ( { 1, 2, 3 }, { 2, 3 }, { 1 } )
%e A060090 and 16 4-block bicoverings:
%e A060090 1 ( { 3 }, { 2 }, { 1 }, { 1, 2, 3 } )
%e A060090 2 ( { 3 }, { 2 }, { 1, 3 }, { 1, 2 } )
%e A060090 3 ( { 3 }, { 2 }, { 1, 2 }, { 1, 3 } )
%e A060090 4 ( { 3 }, { 2 }, { 1, 2, 3 }, { 1 } )
%e A060090 5 ( { 3 }, { 2, 3 }, { 1 }, { 1, 2 } )
%e A060090 6 ( { 3 }, { 2, 3 }, { 1, 2 }, { 1 } )
%e A060090 7 ( { 3 }, { 1, 2 }, { 2 }, { 1, 3 } )
%e A060090 8 ( { 3 }, { 1, 2 }, { 2, 3 }, { 1 } )
%e A060090 9 ( { 3 }, { 1, 2, 3 }, { 2 }, { 1 } )
%e A060090 10 ( { 2, 3 }, { 3 }, { 1 }, { 1, 2 } )
%e A060090 11 ( { 2, 3 }, { 3 }, { 1, 2 }, { 1 } )
%e A060090 12 ( { 2, 3 }, { 1 }, { 3 }, { 1, 2 } )
%e A060090 13 ( { 2, 3 }, { 1 }, { 1, 3 }, { 2 } )
%e A060090 14 ( { 2, 3 }, { 1, 3 }, { 2 }, { 1 } )
%e A060090 15 ( { 2, 3 }, { 1, 3 }, { 1 }, { 2 } )
%e A060090 16 ( { 1, 2, 3 }, { 3 }, { 2 }, { 1 } )
%o A060090 (PARI) seq(n)={my(m=3*n\2, y='y + O('y^(n+1))); Vec(subst(Pol(serlaplace(exp(-x - x^2*y/(2*(1-y)) + O(x*x^m))*sum(k=0, m, 1/(1-y)^binomial(k, 2)*x^k/k!))), x, 1))} \\ _Andrew Howroyd_, Jan 30 2020
%Y A060090 Row n=2 of A331571.
%Y A060090 Row sums of A060092.
%Y A060090 Cf. A060069, A060070, A060051, A060052, A060053, A002718, A059443.
%K A060090 nonn
%O A060090 0,3
%A A060090 _Vladeta Jovovic_, Feb 25 2001