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 A182555 #16 Mar 17 2023 02:03:45 %S A182555 1,2,5,12,29,68,158,360,813,1812,4010,8792,19170,41512,89500,191952, %T A182555 410237,873140,1853042,3919608,8271126,17406072,36556580,76602032, %U A182555 160240594,334554248,697462628,1451633520,3017426468,6263171792,12985655736,26889935776,55626815005,114947516916,237318165314,489482593592,1008787357902,2077219057240,4274204436052 %N A182555 Expansion of g.f. (3-4*x-sqrt(1-4*x^2))/(2*(1-2*x)^2). %H A182555 F. Disanto and S. Rinaldi, <a href="http://www.mat.unisi.it/newsito/puma/public_html/22_1/2-disanto_rinaldi.pdf">Symmetric convex permutominoes and involutions</a>, PU. M. A., Vol. 22 (2011), No. 1, pp. 39-60; See M_n. %F A182555 G.f.: (3-4*x-sqrt(1-4*x^2))/(2*(1-2*x)^2). %F A182555 D-finite with recurrence: n*(n-4)*a(n) +2*(5+2n-n^2)*a(n-1) -4*(n-2)*(n-5)*a(n-2) +8*(n-2)*(n-3)*a(n-3)=0. - _R. J. Mathar_, Jun 28 2012 %F A182555 a(n) ~ n*2^(n-1) * (1-2*sqrt(2/Pi)/sqrt(n)). - _Vaclav Kotesovec_, Jun 29 2013 %K A182555 nonn %O A182555 0,2 %A A182555 _N. J. A. Sloane_, May 05 2012