|
| |
|
|
A112320
|
|
Coefficients of x^n in the (n+1)-th self-composition of (x + x^2) for n>=1.
|
|
4
|
|
|
|
1, 3, 12, 70, 560, 5810, 74760, 1153740, 20817588, 430604724, 10052947476, 261595087182, 7509722346204, 235808741944100, 8040824716606176, 295914258931377276, 11690732617035570008, 493527339623630078552
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
|
OFFSET
|
1,2
|
|
|
LINKS
|
Table of n, a(n) for n=1..18.
|
|
|
FORMULA
|
a(n) = [x^n] F_{n+1}(x) where F_{n+1}(x) = F_n(x+x^2) with F_1(x) = x+x^2 and F_0(x)=x for n>=1.
|
|
|
EXAMPLE
|
Initial terms in self-compositions of (x+x^2) are:
F(x) = x + x^2
F(F(x)) = (1)*x + 2*x^2 + 2*x^3 + x^4
F(F(F(x))) = x + (3)*x^2 + 6*x^3 + 9*x^4 + 10*x^5 +...
F(F(F(F(x)))) = x + 4*x^2 + (12)*x^3 + 30*x^4 + 64*x^5 +...
F(F(F(F(F(x))))) = x + 5*x^2 + 20*x^3 + (70)*x^4 + 220*x^5 +...
F(F(F(F(F(F(x)))))) = x + 6*x^2 + 30*x^3 + 135*x^4 + (560)*x^5 +...
|
|
|
MAPLE
|
{a(n)=local(F=x+x^2, G=x+x*O(x^n)); if(n<1, 0, for(i=1, n+1, G=subst(F, x, G)); return(polcoeff(G, n, x)))}
|
|
|
CROSSREFS
|
Cf. A112317, A112319.
Sequence in context: A125862 A077460 A001205 * A103366 A175836 A020530
Adjacent sequences: A112317 A112318 A112319 * A112321 A112322 A112323
|
|
|
KEYWORD
|
nonn
|
|
|
AUTHOR
|
Paul D. Hanna, Sep 06 2005
|
|
|
STATUS
|
approved
|
| |
|
|
