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 A217894 #36 Sep 08 2022 08:46:04
%S A217894 -23,17,7,97,137,277,367,557,697,937,1127,1417,1657,1997,2287,2677,
%T A217894 3017,3457,3847,4337,4777,5317,5807,6397,6937,7577,8167,8857,9497,
%U A217894 10237,10927,11717,12457,13297,14087,14977,15817,16757,17647,18637,19577,20617,21607
%N A217894 50k^2-20k-23 interleaved with 50k^2+30k+17 for k=>0.
%C A217894 The sequence (the fifth and last in the family) is present as a family of interleaved sequences (five in total) which are separated or factored out to give individual sequences. The first sequence is the parent having the formulas: 50*n^2-100*n+25 and 50*n^2-50*n+25 whose entries are all divisible by 25 and is identical to A178218. The fifth sequence has the formulas 50*n^2-20*n-23 and 50*n^2+30*n+17 and is part of a group where each of the sequences are new, except for the parent (in the factored form).
%H A217894 Vincenzo Librandi, <a href="/A217894/b217894.txt">Table of n, a(n) for n = 0..1000</a>
%H A217894 Eddie Gutierrez <a href="http://oddwheel.com/square_sequencesVIII.html">New Interleaved Sequences Part H</a> or Oddwheel.com, Section B1 Line 28 (square_sequencesVIII.html), Part H.
%H A217894 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,0,-2,1).
%F A217894 G.f.: (-23+63*x-27*x^2+37*x^3)/((1+x)*(1-x)^3).
%F A217894 a(n) = 2*a(n-1)-2*a(n-3)+a(n-4).
%F A217894 a(n) = (10*n*(5*n-4)-75*(-1)^n-1)/4 -4. [_Bruno Berselli_, Oct 15 2012]
%e A217894 a(9) = 2*a(8) - 2*a(6) + a(5) = 1394 - 734 + 277 = 937.
%t A217894 Flatten[Table[{50*n^2 - 20*n - 23, 50*n^2 + 30*n + 17}, {n, 0, 23}]] (* _Bruno Berselli_, Oct 23 2012 *)
%t A217894 CoefficientList[Series[(-23 + 63*x - 27*x ^ 2 + 37*x^3)/((1+x)*(1-x)^3), {x, 0, 50}], x] (* _Vincenzo Librandi_, Nov 23 2012 *)
%o A217894 (Magma) &cat[[50*k^2-20*k-23, 50*k^2+30*k+17]: k in [0..23]]; // _Bruno Berselli_, Oct 23 2012
%o A217894 (PARI) vector(48, n, k=(n-1)\2; if(n%2, 50*k^2-20*k-23, 50*k^2+30*k+17)) \\ _Bruno Berselli_, Oct 23 2012
%Y A217894 Cf. A178218, A214345, A214393, A214405, A216876.
%K A217894 sign,easy
%O A217894 0,1
%A A217894 _Eddie Gutierrez_, Oct 14 2012
%E A217894 Definition rewritten by _Bruno Berselli_, Nov 22 2012