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 A104506 #11 Jan 05 2021 21:47:59
%S A104506 0,-1,-2,0,8,15,-6,-77,-120,117,770,946,-1728,-7735,-6930,22800,76960,
%T A104506 42245,-282150,-751640,-125800,3341205,7145710,-2002725,-38228232,
%U A104506 -65418925,55550014,424605078,566938400,-936604097,-4587287310
%N A104506 Column 1 of triangle A104505, which is equal to the right-hand side of the triangle A084610 of coefficients in (1 + x - x^2)^n.
%H A104506 P. Barry, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL14/Barry3/barry132.html">On the Central Coefficients of Bell Matrices</a>, J. Int. Seq. 14 (2011) # 11.4.3, page 8.
%F A104506 G.f.: ((1-x)/sqrt(1-2*x+5*x^2) - 1)/(2*x).
%F A104506 a(n) = (-1)^n*n*A007440(n) (reversion of g.f. for Fibonacci numbers).
%F A104506 a(n) = -Sum_{k=0..floor(n/2)} C(n, k)*C(n-k, k+1)*(-1)^k. - _Paul Barry_, May 02 2005
%F A104506 E.g.f.: -exp(x)Bessel_I(1,2*i*x)/i, i=sqrt(-1). - _Paul Barry_, Feb 10 2006
%F A104506 -(n-1)*(n+1)*a(n) + n*(2*n-1)*a(n-1) - 5*n*(n-1)*a(n-2) = 0. - _R. J. Mathar_, Aug 17 2017
%o A104506 (PARI) {a(n)=polcoeff(((1-x)/sqrt(1-2*x+5*x^2+x^2*O(x^n))-1)/(2*x),n)}
%Y A104506 Cf. A104505, A007440, A104507, A104508, A104509.
%K A104506 sign
%O A104506 0,3
%A A104506 _Paul D. Hanna_, Mar 11 2005