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 A381121 #10 Feb 16 2025 10:26:02
%S A381121 1,0,1,3,11,47,255,1727,14954,166232,2384053,44182143,1058142319,
%T A381121 32718935706,1304369332319,66936884741385,4414855587293931
%N A381121 Number of partially ordered sets ("posets") covering n unlabeled elements.
%F A381121 a(0) = 1; a(n) = A000112(n) - A000112(n - 1) for n > 0.
%e A381121 For n = 3 there are 5 posets, but 2 of them have at least 1 unrelated element, so there are 5 - 2 = 3 = a(3) posets without an unrelated element.
%Y A381121 Partial differences of A000112.
%K A381121 nonn,hard,more
%O A381121 0,4
%A A381121 _Peter Dolland_, Feb 14 2025