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 A178689 #12 Dec 26 2022 11:31:51
%S A178689 0,0,0,10,253,6384,208887,9673189,651633791,63901292323,9040801794022,
%T A178689 1825884406581355,521181413335003984,208402574279716434454,
%U A178689 115825454535371969786250,88852094572776191675804592
%N A178689 Partial sums of A122836 (number of topologies on n labeled elements in which at least one element belongs to some pair of noncomparable members of the topology).
%C A178689 All listed (the first 16) values are nonprimes. In the underlying sequence, only A122836(5) = 6131 is prime of the listed values.
%F A178689 a(n) = Sum_{i=0..n} A122836(i) = Sum_{i=0..n} (A000798(i) - A122835(i)) = (Sum_{i=0..n} A000798(i)) - (Sum_{i=0..n} A122835(i)).
%e A178689 a(4) = 0 + 0 + 0 + 10 + 243 = 253 = 11 * 23.
%Y A178689 Cf. A000798, A122835, A122836.
%K A178689 nonn
%O A178689 0,4
%A A178689 _Jonathan Vos Post_, Dec 25 2010
%E A178689 a(13)-a(15) corrected by _Georg Fischer_, Dec 26 2022