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 A174325 #28 Sep 11 2022 06:21:18
%S A174325 0,-3,3,45,6,165,63,357,30,621,195,957,72,1365,399,1845,132,2397,675,
%T A174325 3021,210,3717,1023,4485,306,5325,1443,6237,420,7221,1935,8277,552,
%U A174325 9405,2499,10605,702,11877,3135,13221,870,14637,3843,16125,1056,17685,4623,19317
%N A174325 Trisection A061037(3*n-2) of the Balmer spectrum numerators extended to negative indices.
%C A174325 All terms are multiples of 3.
%H A174325 G. C. Greubel, <a href="/A174325/b174325.txt">Table of n, a(n) for n = 0..5000</a>
%H A174325 <a href="/index/Rec#order_12">Index entries for linear recurrences with constant coefficients</a>, signature (0,0,0,3,0,0,0,-3,0,0,0,1).
%F A174325 a(n) = A142600(n-1), n>1.
%F A174325 G.f.: -3*x*(7*x^10 +5*x^9 +39*x^8 +4*x^7 +74*x^6 +18*x^5 +58*x^4 +2*x^3 +15*x^2 +x -1) / ((x -1)^3*(x +1)^3*(x^2 +1)^3). - _Colin Barker_, Oct 15 2014
%F A174325 Sum_{n>=1} 1/a(n) = 11*log(3)/16 - 5*Pi/(48*sqrt(3)) - 1/4. - _Amiram Eldar_, Sep 11 2022
%t A174325 Table[Numerator[(n-2)*(n+2)/(4*n^2)],{n,-2,300,3}] (* _Vaclav Kotesovec_, Oct 15 2014 *)
%o A174325 (PARI) concat(0, Vec(-3*x*(7*x^10 +5*x^9 +39*x^8 +4*x^7 +74*x^6 +18*x^5 +58*x^4 +2*x^3 +15*x^2 +x -1) / ((x -1)^3*(x +1)^3*(x^2 +1)^3) + O(x^100))) \\ _Colin Barker_, Oct 15 2014
%o A174325 (Magma) I:=[0,-3,3,45,6,165,63,357,30,621,195,957]; [n le 12 select I[n] else 3*Self(n-4)-3*Self(n-8)+Self(n-12): n in [1..50]]; // _Vincenzo Librandi_, Oct 15 2014
%Y A174325 Cf. A061037, A142590, A142600.
%K A174325 sign,easy,frac,less
%O A174325 0,2
%A A174325 _Paul Curtz_, Nov 27 2010