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 A349927 #40 Dec 12 2021 13:21:45
%S A349927 0,0,2,43,276,1150,3710,10017,23688,50556,99450,183095,319132,531258,
%T A349927 850486,1316525,1979280,2900472,4155378,5834691,8046500,10918390,
%U A349927 14599662,19263673,25110296,32368500,41299050,52197327,65396268,81269426,100234150
%N A349927 Number of transitive relations on an n-set with exactly three ordered pairs.
%H A349927 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (7,-21,35,-35,21,-7,1).
%F A349927 a(n) = 2*C(n,2) + 37*C(n,3) + 116*C(n,4) + 180*C(n,5) + 120*C(n,6).
%F A349927 a(n) = (1/6)*(n^6 - 6*n^5 + 24*n^4 - 47*n^3 + 38*n^2 - 10*n).
%e A349927 a(2) = 2. These two transitive relations are {(1,1),(1,2),(2,2)} and {(1,1),(2,1),(2,2)} on the 2-set {1,2}.
%o A349927 (PARI) A349927(n) = (1/6)*(n^6 - 6*n^5 + 24*n^4 - 47*n^3 + 38*n^2 - 10*n); \\ _Antti Karttunen_, Dec 05 2021
%Y A349927 Cf. A349919, A349849.
%K A349927 nonn,easy
%O A349927 0,3
%A A349927 _Firdous Ahmad Mala_, Dec 05 2021