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 A227832 #44 Jun 02 2025 08:36:16 %S A227832 1,4,-1,6,-3,8,-5,10,-7,12,-9,14,-11,16,-13,18,-15,20,-17,22,-19,24, %T A227832 -21,26,-23,28,-25,30,-27,32,-29,34,-31,36,-33,38,-35,40,-37,42,-39, %U A227832 44,-41,46,-43,48,-45,50,-47,52,-49 %N A227832 Sum of odd numbers starting with 1, alternating signs (beginning with plus). %C A227832 1st,3rd,5th (odd terms) increase by 2, 2nd,4th,6th,8th (even terms) decrease by 2 each time. %H A227832 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-1,1,1). %F A227832 a(n) = -a(n-1) + a(n-2) + a(n-3). - _Charles R Greathouse IV_, Aug 02 2013 %F A227832 G.f.: x*(2*x^2 + 5*x + 1)/((1-x)*(1+x)^2). a(n) = n*(-1)^n + 2 = A038608(n) + 2. - _Ralf Stephan_, Aug 07 2013 %e A227832 (1+3)=4 (4-5)=-1 (-1+7)=6 (6-9)=-3 (-3+11)=8 (8-13)=-5 (-5+15)=10. %o A227832 (PARI) a(n) = n*(-1)^n + 2; \\ _Michel Marcus_, Feb 08 2016 %Y A227832 Cf. A065164 (absolute values). %K A227832 sign,easy %O A227832 1,2 %A A227832 _D.Wilde_, Aug 02 2013