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A140094 G.f. satisfes: A(x) = x/[1 - A(A(A(x)))] = Series_Reversion[x - x*A(A(x))]. 3
1, 1, 4, 25, 199, 1855, 19387, 221407, 2717782, 35455981, 487672243, 7029980797, 105732907498, 1653377947393, 26805765569863, 449568735630517, 7785116448484318, 138980739891821269, 2554369130466577138 (list; graph; refs; listen; history; internal format)
OFFSET

1,3

LINKS

Paul D. Hanna, Table of n, a(n), n = 1..100.

FORMULA

Define A_{n} such that A_{n+1}(x) = A( A_{n}(x) ) with A_0(x) = x,

then A_{n}(x) = A_{n-1}/[1 - A_{n+2}(x)] ;

thus A_{n}(x) = 1 - A_{n-3}(x) / A_{n-2}(x).

G.f. A(x)/x is the unique solution to variable A in the infinite system of simultaneous equations starting with:

A = 1 + xAC;

B = A + xBD;

C = B + xCE;

D = C + xDF;

E = D + xEG; ...

EXAMPLE

G.f.: A(x) = x + x^2 + 4*x^3 + 25*x^4 + 199*x^5 + 1855*x^6 + 19387*x^7 +...

Self-compositions A_{n+1}(x) = A( A_{n}(x) ) are related as follows.

A_2(x) = 1 - Series_Reversion[A(x)]/x where

A_2(x) = x + 2*x^2 + 10*x^3 + 71*x^4 + 616*x^5 + 6119*x^6 + 67210*x^7 +...

A_3(x) = 1 - x/A(x) where

A_3(x) = x + 3*x^2 + 18*x^3 + 144*x^4 + 1365*x^5 + 14544*x^6 +...;

A_4(x) = 1 - A(x)/A_2(x) where

A_4(x) = x + 4*x^2 + 28*x^3 + 250*x^4 + 2584*x^5 + 29584*x^6 +...

A_5(x) = 1 - A_2(x)/A_3(x) where

A_5(x) = x + 5*x^2 + 40*x^3 + 395*x^4 + 4435*x^5 + 54515*x^6 +...

A_6(x) = 1 - A_3(x)/A_4(x) where

A_6(x) = x + 6*x^2 + 54*x^3 + 585*x^4 + 7104*x^5 + 93555*x^6 +...

Self-compositions are also related by continued fractions:

A(x) = x/(1 - A_2(x)/(1 - A_4(x)/(1 - A_6(x)/(1 -...)))) ;

A_2(x) = A(x)/(1 - A_3(x)/(1 - A_5(x)/(1 - A_7(x)/(1 -...)))).

PROG

(PARI) {a(n)=local(A); if(n<0, 0, n++; A=x+O(x^2); for(i=2, n, A=x/(1-subst(A, x, subst(A, x, A)))); polcoeff(A, n))}

CROSSREFS

Cf. A140095, A088714.

Cf. A088717, A091713, A120971, A139702.

Sequence in context: A202827 A065735 A182953 * A144647 A060910 A195260

Adjacent sequences:  A140091 A140092 A140093 * A140095 A140096 A140097

KEYWORD

nonn

AUTHOR

Paul D. Hanna (pauldhanna(AT)juno.com), May 08 2008, May 20 2008

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Last modified February 15 17:46 EST 2012. Contains 205835 sequences.