OFFSET
0,5
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..200
FORMULA
Define the sequence b(n,m) as follows. If n<m, b(n,m) = 0, else if n=m, b(n,m) = 1, otherwise b(n,m) = 1/6 * ( 6^(n-m) * Sum_{l=0..m} binomial(l,n-3*m+2*l) * binomial(m,l) - Sum_{l=m+1..n-1} (b(n,l) + Sum_{k=l..n} (b(n,k) + Sum_{j=k..n} (b(n,j) + Sum_{i=j..n} (b(n,i) + Sum_{h=i..n} b(n,h) * b(h,i)) * b(i,j)) * b(j,k)) * b(k,l)) * b(l,m) ). a(n) = b(n,1).
Let B(x) = A(A(x)) and C(x) = A(A(A(x))).
B(B(B(x))) = C(C(x)) = x + 6*x^2 + 36*x^3.
B(x) = F(2*x)/2, where F(x) is the g.f. for A220288.
C(x) = G(3*x)/3, where G(x) is the g.f. for A220110.
EXAMPLE
A(A(x)) = x + 2*x^2 + 4*x^3 - 64*x^4 + 448*x^5 - 832*x^6 - 24704*x^7 + ...
A(A(A(x))) = x + 3*x^2 + 9*x^3 - 81*x^4 + 405*x^5 + 243*x^6 - 28431*x^7 + ...
CROSSREFS
KEYWORD
sign
AUTHOR
Seiichi Manyama, May 04 2024
STATUS
approved