login
A168505
Expansion of 1/(1-x/(1+x/(1-x/(1-x/(1+x/(1-x/(1-x/(1+x/(1-... (continued fraction).
2
1, 1, 0, -1, -2, -2, 0, 5, 12, 16, 6, -32, -102, -170, -130, 199, 966, 1978, 2192, -650, -9292, -23624, -33760, -12138, 84440, 280852, 493932, 397668, -639676, -3248464, -6947460, -8068587, 2165980, 35591960, 94129446, 139864828, 56393482, -352505722
OFFSET
0,5
COMMENTS
Hankel transform is A131561(n+1). First column of array whose production matrix begins
1, 1;
-1, 0, 1;
0, 1, 0, 1;
0, 0, -1, 2, 1;
0, 0, 0, -1, 0, 1;
0, 0, 0, 0, 1, 0, 1;
0, 0, 0, 0, 0, -1, 2, 1;
FORMULA
G.f.: 1/(1-x+x^2/(1-x^2/(1+x^2/(1-2x+x^2/(1-x^2/(1+x^2/(1-2x+x^2/(1-x^2/(1+... (continued fraction, defined by
the sequences (1,0,0,2,0,0,2,0,0,2,0,...) and (-1,1,-1,-1,1,-1,...);
g.f.: (1+x-sqrt(1-2x+x^2+4x^3))/(2x(1-x)).
a(n) = Sum_{k=0..n} A198379(n,k)*(-1)^(n-k). - Philippe Deléham, Oct 29 2011
a(n) = (-1)^n*Sum_{k=0..n} A174014(n,k)*(-2)^k. - Philippe Deléham, Feb 16 2012
G.f.: (1+x)/(G(0)+x), where G(k)= 1 - x + x^3/G(k+1); (continued fraction). - Sergei N. Gladkovskii, Jul 29 2013
Conjecture: (n+1)*a(n) - 3*n*a(n-1) + 3*(n-1)*a(n-2) + 3*(n-4)*a(n-3) + 2*(-2*n+7)*a(n-4) = 0. - R. J. Mathar, Feb 10 2015
G.f. A(x) satisfies (A(x) - 1) / A(x)^2 = (x - x^2) / (1 + x). - Michael Somos, Jan 20 2017
0 = a(n)*(+16*a(n+1) - 6*a(n+2) - 42*a(n+3) + 54*a(n+4) - 22*a(n+5)) + a(n+1)*(-18*a(n+1) + 27*a(n+2) + 6*a(n+3) - 31*a(n+4) + 18*a(n+5))+ a(n+2)*(-18*a(n+2) + 36*a(n+3) - 30*a(n+4) + 9*a(n+5)) + a(n+3)*(+6*a(n+4) - 6*a(n+5)) + a(n+4)*(+a(n+5)) if n >= 0. - Michael Somos, Jan 20 2017
EXAMPLE
G.f. = 1 + x - x^3 - 2*x^4 - 2*x^5 + 5*x^7 + 12*x^8 + 16*x^9 + 6*x^10 + ...
PROG
(PARI) {a(n) = if( n<0, 0, polcoeff( (1 + x - sqrt(1 - 2*x + x^2 + 4*x^3 + x^2 * O(x^n))) / (2*x*(1 - x)), n))}; /* Michael Somos, Jan 20 2017 */
CROSSREFS
Sequence in context: A222128 A088972 A355570 * A100334 A277295 A254749
KEYWORD
easy,sign
AUTHOR
Paul Barry, Nov 27 2009
STATUS
approved