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 A137224 #15 Sep 26 2024 23:34:56
%S A137224 0,1,2,1,4,5,10,9,16,17,26,25,36,37,50,49,64,65,82,81,100,101,122,121,
%T A137224 144,145,170,169,196,197,226,225,256,257,290,289,324,325,362,361,400,
%U A137224 401,442,441,484,485,530,529,576,577,626,625,676,677,730,729,784
%N A137224 Interleave 4*n^2, 1+4*n^2, 1+(2n+1)^2, (2n+1)^2 (or A016742, A053755, A069894, A016754).
%H A137224 Colin Barker, <a href="/A137224/b137224.txt">Table of n, a(n) for n = 0..1000</a>
%H A137224 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (1,1,-1,1,-1,-1,1).
%F A137224 From _Colin Barker_, Apr 01 2018: (Start)
%F A137224 G.f.: x*(1 + x - 2*x^2 + 2*x^3 + x^4 + x^5) / ((1 - x)^3*(1 + x)^2*(1 + x^2)).
%F A137224 a(n) = a(n-1) + a(n-2) - a(n-3) + a(n-4) - a(n-5) - a(n-6) + a(n-7) for n>6.
%F A137224 (End)
%t A137224 Flatten[Table[{4n^2,4n^2+1,(2n+1)^2+1,(2n+1)^2},{n,0,20}]] (* or *) LinearRecurrence[{1,1,-1,1,-1,-1,1},{0,1,2,1,4,5,10},80] (* _Harvey P. Dale_, Mar 18 2016 *)
%o A137224 (PARI) concat(0, Vec(x*(1 + x - 2*x^2 + 2*x^3 + x^4 + x^5) / ((1 - x)^3*(1 + x)^2*(1 + x^2)) + O(x^60))) \\ _Colin Barker_, Apr 01 2018
%Y A137224 Cf. A016742, A016754, A053755, A069894.
%K A137224 nonn,easy
%O A137224 0,3
%A A137224 _Paul Curtz_, Apr 05 2008