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 A270810 #46 Sep 08 2022 08:46:16 %S A270810 0,1,2,6,16,36,76,156,316,636,1276,2556,5116,10236,20476,40956,81916, %T A270810 163836,327676,655356,1310716,2621436,5242876,10485756,20971516, %U A270810 41943036,83886076,167772156,335544316,671088636,1342177276,2684354556,5368709116,10737418236,21474836476 %N A270810 Expansion of (x - x^2 + 2*x^3 + 2*x^4)/(1 - 3*x + 2*x^2). %H A270810 Colin Barker, <a href="/A270810/b270810.txt">Table of n, a(n) for n = 0..1000</a> %H A270810 M. Diepenbroek, M. Maus, A. Stoll, <a href="http://www.valpo.edu/mathematics-statistics/files/2014/09/Pudwell2015.pdf">Pattern Avoidance in Reverse Double Lists</a>, Preprint 2015. See Table 3. %H A270810 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2). %F A270810 G.f.: x*(1 - x + 2*x^2 + 2*x^3)/((1 - x)*(1 - 2*x)). %F A270810 a(n) = 5*2^(n-2)-4 for n>2. - _Bruno Berselli_, Apr 08 2016 %F A270810 a(n) = 3*a(n-1)-2*a(n-2) for n>4. - _Colin Barker_, Apr 12 2016 %F A270810 From _Paul Curtz_, Sep 23 2019: (Start) %F A270810 a(n+1) = b(n+4) - b(n) where b(n) = 0, 1, 1, 1 followed by A026646. %F A270810 a(n) = 2*a(n-1)+4 for n>4. (End) %o A270810 (Magma) [n le 2 select n else 5*2^(n-2)-4: n in [0..40]]; // _Bruno Berselli_, Apr 08 2016 %o A270810 (PARI) concat(0, Vec(x*(1-x+2*x^2+2*x^3)/((1-x)*(1-2*x)) + O(x^50))) \\ _Colin Barker_, Apr 12 2016 %Y A270810 Agrees with A048487 except for initial terms. %Y A270810 Cf. A002605, A265106, A265107, A265278. %Y A270810 Cf. A026646, A000225. %K A270810 nonn,easy %O A270810 0,3 %A A270810 _N. J. A. Sloane_, Apr 06 2016