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 A283439 #18 Mar 09 2017 10:09:35
%S A283439 1,-3,-9,-6,10,25,15,-21,-49,-28,36,81,45,-55,-121,-66,78,169,91,-105,
%T A283439 -225,-120,136,289,153,-171,-361,-190,210,441,231,-253,-529,-276,300,
%U A283439 625,325,-351,-729,-378,406,841,435,-465,-961,-496,528,1089,561,-595,-1225
%N A283439 Hankel transform of A033434.
%C A283439 a(n) modulo 2 is A131719(n+2).
%F A283439 G.f.: (1 - 5*x + 2*x^3 - 3*x^4 + 2*x^5 - x^6)/((1 + x)*(1 - x + x^2)^3).
%F A283439 a(3*k) = (-1)^k*(k + 1)*(2*k + 1).
%F A283439 a(3*k + 1) = -(-1)^k*(k + 1)*(2*k + 3).
%F A283439 a(3*k + 2) = -(-1)^k*(k + 3)^2.
%t A283439 CoefficientList[Series[(1 - 5*x + 2*x^3 - 3*x^4 + 2*x^5 - x^6)/((1 + x)*(1 - x + x^2)^3) ,{x, 0, 35}], x] (* _Indranil Ghosh_, Mar 08 2017 *)
%o A283439 (PARI) print(Vec((1 - 5*x + 2*x^3 - 3*x^4 + 2*x^5 - x^6)/((1 + x)*(1 - x + x^2)^3) + O(x^36))); \\ _Indranil Ghosh_, Mar 08 2017
%Y A283439 Cf. A131719, A033434.
%K A283439 sign,easy
%O A283439 0,2
%A A283439 _Paul Barry_, Mar 07 2017
%E A283439 More terms from _Indranil Ghosh_, Mar 08 2017