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 A147657 #17 Dec 13 2022 05:44:30
%S A147657 1,2,1,-2,-2,2,3,-2,-4,2,5,-2,-6,2,7,-2,-8,2,9,-2,-10,2,11,-2,-12,2,
%T A147657 13,-2,-14,2,15,-2,-16,2,17,-2,-18,2,19,-2,-20,2,21,-2,-22,2,23,-2,
%U A147657 -24,2,25,-2,-26,2,27,-2,-28,2,29,-2,-30,2,31,-2,-32,2,33
%N A147657 a(1)=1, a(2)=2, thereafter (1, -2, 3, -4, 5, -6, ...) interleaved with (-2, 2, -2, 2, ...).
%C A147657 Equals POLYMOTZKINTINV [1,2,3,...], such that POLYMOTZKINT A147657 = [1,2,3,...]. A comment accompanying the POLYMOTZKINT operation may be found in A005717.
%H A147657 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,-2,0,-1).
%F A147657 (1, -2, 3, -4, 5,...) interleaved with (1, 2, -2, 2,...) such that the first subsequence starts after the first "2" in the second subsequence.
%F A147657 G.f.: x + x^2*(2+x+2*x^2)/(1+x^2)^2. - _R. J. Mathar_, Dec 13 2022
%t A147657 Join[{1,2}, LinearRecurrence[{0, -2, 0, -1}, {1, -2, -2, 2}, 65]] (* _Georg Fischer_, Nov 02 2021 *)
%Y A147657 Cf. A005717, A147658.
%K A147657 easy,sign
%O A147657 1,2
%A A147657 _Gary W. Adamson_, Nov 09 2008
%E A147657 Definition and a(28) ff. corrected by _Georg Fischer_, Nov 02 2021