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 A138739 G.f. A(x) satisfies: A(A(x)) = 3*A(x) - 2*x - x^2 with A(0)=0. 6
 1, 1, 2, 11, 88, 888, 10572, 143214, 2159154, 35702442, 640873656, 12394383780, 256762580460, 5671209169168, 133041670286160, 3304034094162183, 86616702087692256, 2390831825522972392, 69323685702986714272, 2107073248164657741448, 67003070810599639419680, 2225053954972969636237280, 77034579373254666948386880, 2776183496539544726567249520 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS All self-compositions of A(x) may be expressed as a finite sum involving powers of A(x) and x. LINKS Paul D. Hanna, Table of n, a(n) for n = 1..300 EXAMPLE G.f.: A(x) = x + x^2 + 2*x^3 + 11*x^4 + 88*x^5 + 888*x^6 + 10572*x^7 + 143214*x^8 + 2159154*x^9 + 35702442*x^10 + 640873656*x^11 + 12394383780*x^12 + 256762580460*x^13 + 5671209169168*x^14 + 133041670286160*x^15 +... A(A(x)) = x + 2*x^2 + 6*x^3 + 33*x^4 + 264*x^5 + 2664*x^6 + 31716*x^7 + 429642*x^8 + 6477462*x^9 + 107107326*x^10 + 1922620968*x^11 + 37183151340*x^12 + 770287741380*x^13 + 17013627507504*x^14 + 399125010858480*x^15 +... so that A(A(x)) + 2*x + x^2 = 3*A(x). Self-compositions of A=A(x) may be expressed in terms of A and x: A(A(x)) = 3*A - 2*x - x^2 ; A(A(A(x))) = (7*A - A^2) - 6*x - 3*x^2 ; A(A(A(A(x)))) = (15*A - 12*A^2) + (-14 + 12*A)*x + (-11 + 6*A)*x^2 - 4*x^3 - x^4 ; A(A(A(A(A(x))))) = (31*A - 83*A^2 + 14*A^3 - A^4) + (-12*A^2 + 120*A - 30)*x + (-6*A^2 + 60*A - 63)*x^2 - 48*x^3 - 12*x^4 . PROG (PARI) {a(n)=local(A=x+x^2); if(n<1, 0, for(i=3, n+1, A=A+polcoeff(subst(A, x, A+x*O(x^i)), i)*x^i); polcoeff(A, n))} for(n=1, 20, print1(a(n), ", ")) CROSSREFS Cf. A138740. Sequence in context: A036076 A047797 A107096 * A216831 A221864 A197900 Adjacent sequences:  A138736 A138737 A138738 * A138740 A138741 A138742 KEYWORD nonn AUTHOR Paul D. Hanna, Mar 27 2008 STATUS approved

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Last modified June 5 16:19 EDT 2020. Contains 334852 sequences. (Running on oeis4.)