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 A065889 #23 Jan 09 2025 15:43:37
%S A065889 3,60,1080,20580,430080,9920232,252000000,7015381560,212840939520,
%T A065889 6998969586180,248180493969408,9445533398437500,384213343210045440,
%U A065889 16639691095281974160,764619269867445288960,37163398969133506235952,1905131520000000000000000
%N A065889 a(n) = number of unicyclic connected simple graphs whose cycle has length 4.
%H A065889 Alois P. Heinz, <a href="/A065889/b065889.txt">Table of n, a(n) for n = 4..150</a>
%F A065889 E.g.f.: T^4/8, where T = T(x) is Euler's tree function (see A000169).
%F A065889 a(n) = (n-1)*(n-2)*(n-3)*n^(n-4)/2. - _Vladeta Jovovic_, Oct 26 2004
%F A065889 a(n) = 3 * A053508(n). - _Alois P. Heinz_, Jan 09 2025
%t A065889 Table[12*Binomial[n,4]*n^(n-5), {n,4,25}] (* _G. C. Greubel_, May 16 2019 *)
%o A065889 (PARI) {a(n) = 12*binomial(n,4)*n^(n-5)}; \\ _G. C. Greubel_, May 16 2019
%o A065889 (Magma) [12*Binomial(n,4)*n^(n-5) : n in [4..25]]; // _G. C. Greubel_, May 16 2019
%o A065889 (Sage) [12*binomial(n,4)*n^(n-5) for n in (4..25)] # _G. C. Greubel_, May 16 2019
%o A065889 (GAP) List([4..25], n-> 12*Binomial(n,4)*n^(n-5)); # _G. C. Greubel_, May 16 2019
%Y A065889 A065888 ( = 2*A065889) counts sagittal graphs with one cycle (length 4).
%Y A065889 A column of A098909, A053507.
%Y A065889 Main diagonal of A144209.
%Y A065889 Cf. A053508.
%K A065889 nonn
%O A065889 4,1
%A A065889 _Len Smiley_, Nov 27 2001