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 A060491 #12 Nov 26 2022 20:27:39
%S A060491 1,0,0,184,17488,2780752,689187720,236477490418,107317805999204,
%T A060491 62318195302890305,45081693413563797127,39762626850034005271588,
%U A060491 42009504510315968282400843,52381340312720286113688037624,76118747309505733406576769607755
%N A060491 Number of ordered tricoverings of an unlabeled n-set.
%C A060491 A covering of a set is a tricovering if every element of the set is covered by exactly three blocks of the covering.
%H A060491 Andrew Howroyd, <a href="/A060491/b060491.txt">Table of n, a(n) for n = 0..100</a>
%F A060491 E.g.f. for ordered k-block tricoverings of an unlabeled n-set is exp(-x+x^2/2+x^3/3*y/(1-y))*Sum_{k=0..inf}1/(1-y)^binomial(k, 3)*exp(-x^2/2*1/(1-y)^n)*x^k/k!.
%e A060491 There are 184 ordered tricoverings of an unlabeled 3-set: 4 4-block, 60 5-block and 120 6-block tricoverings (cf. A060492).
%o A060491 (PARI) seq(n)={my(m=2*n\2, y='y + O('y^(n+1))); Vec(subst(Pol(serlaplace(exp(-x + x^2/2 + x^3*y/(3*(1-y)) + O(x*x^m))*sum(k=0, m, 1/(1-y)^binomial(k, 3)*exp((-x^2/2)/(1-y)^k + O(x*x^m))*x^k/k!))), x, 1))} \\ _Andrew Howroyd_, Jan 30 2020
%Y A060491 Row n=3 of A331571.
%Y A060491 Row sums of A060492.
%Y A060491 Cf. A060486, A060487, A060090, A060092, A060069, A060070, A060051, A060052, A060053, A002718, A059443.
%K A060491 nonn
%O A060491 0,4
%A A060491 _Vladeta Jovovic_, Mar 20 2001
%E A060491 Terms a(11) and beyond from _Andrew Howroyd_, Jan 30 2020