OFFSET
0,3
LINKS
Paul D. Hanna, Table of n, a(n) for n = 0..200
FORMULA
G.f. satisfies: A(x) = G(x/A(x)^2) where G(x) = A(x*G(x)^2) is the g.f. of A006319 (royal paths in a lattice).
G.f. satisfies: A(x) = sqrt( x/Series_Reversion( x*C(x/(1-x)^2)^2 ) ) where C(x) = 1 + x*C(x)^2 = (1-sqrt(1-4*x))/(2*x) is the g.f. of the Catalan numbers (A000108).
G.f. satisfies: A(x) = A(x)*A(-x) + x/A(x).
EXAMPLE
G.f.: A(x) = 1 + x + 2*x^2 - x^3 - 10*x^4 + 7*x^5 + 88*x^6 - 68*x^7 +...
where
x/A(-x)^2 = x + 2*x^2 - x^3 - 10*x^4 + 7*x^5 + 88*x^6 - 68*x^7 +...
A(x)^2 = 1 + 2*x + 5*x^2 + 2*x^3 - 18*x^4 - 10*x^5 + 151*x^6 + 88*x^7 +...
The g.f. G(x) of A006319 begins:
G(x) = 1 + x + 4*x^2 + 16*x^3 + 68*x^4 + 304*x^5 + 1412*x^6 + 6752*x^7 +...
where G(x) = A(x*G(x)^2) and G(x/A(x)^2) = A(x);
also, G(x) = F(x/(1-x)^2) where F(x) = 1 + x*F(x)^2 is g.f. of A000108:
F(x) = 1 + x + 2*x^2 + 5*x^3 + 14*x^4 + 42*x^5 + 132*x^6 + 429*x^7 +...
PROG
(PARI) {a(n)=local(A=1+x); for(i=1, n, A=1+x/subst(A^2, x, -x+x*O(x^n))); polcoeff(A, n)}
for(n=0, 40, print1(a(n), ", "))
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, Jun 07 2012
STATUS
approved