OFFSET
0,2
COMMENTS
More generally, if G(x) satisfies
G(x) = (1 + a*x*G(x))^m * (1 + b*x*G(x)^2), then
G(x) = (1/x) * Series_Reversion( x * (1 - b*x*(1 + a*x)^m) / (1 + a*x)^m ).
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..903
FORMULA
G.f.: (1/x) * Series_Reversion( x * (1 - x*(1+x)^3) / (1+x)^3 ).
a(n) = (1/(n+1)) * Sum_{k=0..n} binomial(n+k,k) * binomial(3*n+3*k+3,n-k). - Seiichi Manyama, Jan 27 2024
EXAMPLE
G.f.: A(x) = 1 + 4*x + 26*x^2 + 210*x^3 + 1901*x^4 + 18445*x^5 + 187524*x^6 + 1971672*x^7 + 21263360*x^8 +...
PROG
(PARI) {a(n) = my(A=1); for(i=1, n, A = (1 + x*A)^3 * (1 + x*A^2) + x*O(x^n) ); polcoeff(A, n)}
for(n=0, 30, print1(a(n), ", "))
(PARI) {a(n) = my(A=1); A = (1/x)*serreverse(x*(1-x*(1+x)^3)/(1+x +x^2*O(x^n) )^3 ); polcoeff(A, n)}
for(n=0, 30, print1(a(n), ", "))
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Aug 02 2016
STATUS
approved