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 A269440 #11 Feb 16 2025 08:33:30
%S A269440 0,-1,9,-25,55,-100,166,-254,370,-515,695,-911,1169,-1470,1820,-2220,
%T A269440 2676,-3189,3765,-4405,5115,-5896,6754,-7690,8710,-9815,11011,-12299,
%U A269440 13685,-15170,16760,-18456,20264,-22185,24225,-26385,28671,-31084,33630,-36310,39130
%N A269440 Alternating sum of 9-gonal (or decagonal) pyramidal numbers.
%H A269440 OEIS Wiki, <a href="http://oeis.org/wiki/Figurate_numbers">Figurate numbers</a>
%H A269440 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/PyramidalNumber.html">Pyramidal Number</a>
%H A269440 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (-3,-2,2,3,1).
%F A269440 G.f.: x*(1 - 6*x)/((x - 1)*(x + 1)^4).
%F A269440 a(n) = (-1)^n*(2*n - 1)*(14*n^2 + 34*n + 15)/48 + 5/16.
%F A269440 a(n) = Sum_{k = 0..n} (-1)^k*A007584(k).
%t A269440 Table[(-1)^n (2 n - 1) ((14 n^2 + 34 n + 15)/48) + 5/16, {n, 0, 40}]
%t A269440 LinearRecurrence[{-3, -2, 2, 3, 1}, {0, -1, 9, -25, 55}, 41]
%Y A269440 Cf. A000292, A002717, A007584, A173196, A266677.
%K A269440 sign,easy
%O A269440 0,3
%A A269440 _Ilya Gutkovskiy_, Feb 26 2016