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 A051305 #10 Sep 08 2022 08:44:59
%S A051305 0,0,0,0,0,543,118629,12564636,907001550,51751693161,2527016053023,
%T A051305 110737868741742,4489929936371880,171944175793168779,
%U A051305 6309813148166785257,224210698542088771968
%N A051305 Number of 5-element proper antichains of an n-element set.
%H A051305 G. C. Greubel, <a href="/A051305/b051305.txt">Table of n, a(n) for n = 0..660</a>
%F A051305 a(n) = (1/5!)*(32^n -30*24^n +150*20^n -45*18^n +85*17^n -515*16^n -450*15^n +1365*14^n +390*13^n -1680*12^n -22*11^n +1875*10^n -1080*9^n -685*8^n +980*7^n -669*6^n +575*5^n -195*4^n -150*3^n +124*2^n -24).
%t A051305 Table[(32^n - 30*24^n + 150*20^n - 45*18^n + 85*17^n - 515*16^n -450*15^n + 1365*14^n + 390*13^n - 1680*12^n - 22*11^n + 1875*10^n - 1080*9^n - 685*8^n + 980*7^n - 669*6^n + 575*5^n - 195*4^n - 150*3^n + 124*2^n - 24)/5!, {n, 0, 50}] (* _G. C. Greubel_, Oct 07 2017 *)
%o A051305 (PARI) for(n=0,50, print1((32^n - 30*24^n + 150*20^n - 45*18^n + 85*17^n - 515*16^n -450*15^n + 1365*14^n + 390*13^n - 1680*12^n - 22*11^n + 1875*10^n - 1080*9^n - 685*8^n + 980*7^n - 669*6^n + 575*5^n - 195*4^n - 150*3^n + 124*2^n - 24)/5!, ", ")) \\ _G. C. Greubel_, Oct 07 2017
%o A051305 (Magma) [(32^n - 30*24^n + 150*20^n - 45*18^n + 85*17^n - 515*16^n -450*15^n + 1365*14^n + 390*13^n - 1680*12^n - 22*11^n + 1875*10^n - 1080*9^n - 685*8^n + 980*7^n - 669*6^n + 575*5^n - 195*4^n - 150*3^n + 124*2^n - 24)/(120): n in [0..50]]; // _G. C. Greubel_, Oct 07 2017
%Y A051305 Cf. A032263, A036239, A051112.
%K A051305 nonn
%O A051305 0,6
%A A051305 _Vladeta Jovovic_, Goran Kilibarda, Zoran Maksimovic