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 A022997 #20 Jul 08 2025 17:10:56
%S A022997 0,15,28,135,132,455,360,1071,760,2079,1380,3575,2268,5655,3472,8415,
%T A022997 5040,11951,7020,16359,9460,21735,12408,28175,15912,35775,20020,44631,
%U A022997 24780,54839,30240,66495,36448,79695,43452,94535,51300,111111,60040,129519,69720,149855
%N A022997 Numerator of n*(n-2)*(2*n-1)/(2*(n-1)).
%H A022997 Amiram Eldar, <a href="/A022997/b022997.txt">Table of n, a(n) for n = 2..10000</a>
%H A022997 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (0,4,0,-6,0,4,0,-1).
%F A022997 G.f.: x^3*(x^6+5x^4+20x^3+75x^2+28x+15)/((x-1)^4*(x+1)^4). - _Ralf Stephan_, Sep 03 2003
%F A022997 Sum_{n>=3} 1/a(n) = 11/9 + Pi/6 - 7*log(2)/3. - _Amiram Eldar_, Sep 21 2023
%e A022997 Fractions begins with 0, 15/4, 28/3, 135/8, 132/5, 455/12, 360/7, 1071/16, 760/9, 2079/20, 1380/11, 3575/24, ...
%t A022997 a[n_] := Numerator[n*(n - 2)*(2*n - 1)/(2*(n - 1))]; Array[a, 50, 2] (* _Amiram Eldar_, Sep 21 2023 *)
%o A022997 (PARI) a(n) = numerator(n*(n-2)*(2*n-1)/(2*(n-1))); \\ _Amiram Eldar_, Sep 21 2023
%Y A022997 Cf. A022998 (denominators, with an offset shift).
%K A022997 nonn,easy,frac
%O A022997 2,2
%A A022997 _N. J. A. Sloane_
%E A022997 More terms from _Amiram Eldar_, Sep 21 2023