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 A112986 #28 May 15 2024 01:30:51
%S A112986 0,0,0,3,5,7,18,22,26,45,51,57,84,92,100,135,145,155,198,210,222,273,
%T A112986 287,301,360,376,392,459,477,495,570,590,610,693,715,737,828,852,876,
%U A112986 975,1001,1027,1134,1162,1190,1305,1335,1365,1488,1520,1552,1683,1717,1751,1890
%N A112986 Crossing number of K_{4,n} on the real projective plane.
%H A112986 Pak Tung Ho, <a href="http://dx.doi.org/10.1016/j.disc.2005.09.010">The crossing number of K_{4,n} on the real projective plane</a>, Discr. Math., 304 (2005), pp. 23-33.
%H A112986 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,0,2,-2,0,-1,1).
%F A112986 a(n) = floor(n/3)*(2*n-3). [Corrected by _Amiram Eldar_, May 15 2024]
%F A112986 G.f.: -x^3*(5*x^3+2*x^2+2*x+3) / ((x-1)^3*(x^2+x+1)^2). - _Colin Barker_, Mar 06 2014
%F A112986 Sum_{n>=3} 1/a(n) = 2*log(2)/3 + 6 - sqrt(3)*Pi. - _Amiram Eldar_, May 15 2024
%t A112986 a[n_] := Floor[n/3]*(2*n - 3); Array[a, 100, 0] (* _Amiram Eldar_, May 15 2024 *)
%Y A112986 Cf. A008724.
%K A112986 nonn,easy
%O A112986 0,4
%A A112986 _N. J. A. Sloane_, Dec 24 2005