OFFSET
0,1
COMMENTS
For the notion Z-sequence for a Riordan triangle (lower triangular matrix) R(n,m) see a W.Lang link under A006232, with references. The Z-sequence appears in the recurrence for any entry R(n,0), n >= 1: R(n,0) = sum(Z(m)*R(n-1,m), m=0..n-1).
FORMULA
O.g.f.: (1 - (2 - c(-x))/(1 + 4*x))/(1 - c(-x)) = ((3 + 4*x) + 4*x*c(-x))/(1 + 4*x), with c(x) the o.g.f. of A000108 (Catalan).
a(0) = 3, a(n) = ((-1)^n)*4*binomial(2*n-1,n), n >= 1, (from adding the two pieces of the second o.g.f. version).
|a(n)| = A100320(n), n >0. - R. J. Mathar, Apr 22 2013
G.f.: 1 + G(0), where G(k)= 1 + 1/(1 - 2*x*(2*k+1)/(2*x*(2*k+1) - (k+1)/G(k+1))); (continued fraction). - Sergei N. Gladkovskii, May 24 2013
CROSSREFS
KEYWORD
sign,easy
AUTHOR
Wolfdieter Lang, Oct 18 2012
STATUS
approved