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 A327610 #8 Sep 30 2019 11:59:27 %S A327610 0,0,1,4,14,49,154,496,1520,4705,14266,43384,130844,394849,1187614, %T A327610 3571936,10729040,32222785,96724306,290313064,871172324,2614069249, %U A327610 7843168774,23531688976,70598997560,211805640865,635432906746,1906333059544,5719063904204 %N A327610 Number of length n reversible string structures that are not palindromic using exactly three different colors. %H A327610 Andrew Howroyd, <a href="/A327610/b327610.txt">Table of n, a(n) for n = 1..200</a> %H A327610 <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (6,-6,-24,49,6,-66,36). %F A327610 a(n) = A056327 - A000392(ceiling(n/2)). %F A327610 a(n) = 6*a(n-1) - 6*a(n-2) - 24*a(n-3) + 49*a(n-4) + 6*a(n-5) - 66*a(n-6) + 36*a(n-7) for n > 7. %F A327610 G.f.: x^3*(1 - 2*x - 4*x^2 + 13*x^3 - 9*x^4)/((1 - x)*(1 - 2*x)*(1 - 3*x)*(1 - 2*x^2)*(1 - 3*x^2)). %o A327610 (PARI) concat([0,0], Vec((1 - 2*x - 4*x^2 + 13*x^3 - 9*x^4)/((1 - x)*(1 - 2*x)*(1 - 3*x)*(1 - 2*x^2)*(1 - 3*x^2)) + O(x^30))) %Y A327610 Column k=3 of A309748. %Y A327610 Cf. A000392, A056327, A284949, A327611. %K A327610 nonn,easy %O A327610 1,4 %A A327610 _Andrew Howroyd_, Sep 18 2019