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 A216876 #42 Sep 08 2022 08:46:03
%S A216876 -5,5,-5,25,35,85,115,185,235,325,395,505,595,725,835,985,1115,1285,
%T A216876 1435,1625,1795,2005,2195,2425,2635,2885,3115,3385,3635,3925,4195,
%U A216876 4505,4795,5125,5435,5785,6115,6485,6835,7225,7595,8005,8395,8825,9235,9685
%N A216876 20k^2-20k-5 interleaved with 20k^2+5 for k=>0.
%C A216876 The sequence (the second in the family) is present as a family of single interleaved sequence of which are separated or factored out of the larger sequence to give individual sequences. The larger sequence produces two smaller interleaved sequences where one of them has the formula above and a first interleaved sequence. There are a total of two sequences in this family.
%H A216876 Eddie Gutierrez <a href="http://www.oddwheel.com/square_sequencesV.html">New Interleaved Sequences Part E</a> on oddwheel.com, Section B1 Line No. 25 (square_sequencesV.html), Part E.
%H A216876 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1).
%F A216876 Contribution from _Bruno Berselli_, Sep 27 2012: (Start)
%F A216876 G.f.: -5*(1-3*x+3*x^2-5*x^3)/((1+x)*(1-x)^3).
%F A216876 a(n) = (5/2)*(2*n*(n-2)-3*(-1)^n+1).
%F A216876 a(n) = 5*A214345(n-3) with A214345(-3)=-1, A214345(-2)=1, A214345(-1)=-1. (End)
%t A216876 Flatten[Table[{20*n^2 - 20*n - 5, 20*n^2 + 5}, {n, 0, 30}]] (* _T. D. Noe_, Sep 26 2012 *)
%o A216876 (Magma) &cat[[20*k^2-20*k-5, 20*k^2+5]: k in [0..22]]; // _Bruno Berselli_, Sep 27 2012
%o A216876 (PARI) vector(60,n,k=(n-1)\2;if(n%2,20*k^2-20*k-5,20*k^2+5)) \\ _Charles R Greathouse IV_, Sep 27 2012
%o A216876 (Maxima) A216876(n):=(5/2)*(2*n*(n-2)-3*(-1)^n+1)$
%o A216876 makelist(A216876(n),n,0,30); /* _Martin Ettl_, Nov 01 2012 */
%Y A216876 Cf. A178218, A214345, A214493, A214393, A214405, A216871.
%K A216876 sign,easy
%O A216876 0,1
%A A216876 _Eddie Gutierrez_, Sep 18 2012
%E A216876 More terms from _T. D. Noe_, Sep 26 2012
%E A216876 Definition rewritten by _Bruno Berselli_, Oct 25 2012