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A171191 G.f. satisfies: A(x) = exp( Sum_{n>=1} [A(x)^n + 1/A(-x)^n]*x^n/n ). 2
1, 2, 7, 20, 73, 263, 1111, 4451, 20161, 85304, 401401, 1755593, 8465311, 37866818, 185756605, 844627115, 4196759383, 19321634594, 96962969047, 450810982796, 2280344734891, 10686378006479, 54406554842287, 256637809742444 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..23.

FORMULA

G.f. satisfies: A(x) = 1/[(1 - x*A(x))*(1 - x/A(-x))]. - Paul D. Hanna, Dec 06 2009

EXAMPLE

G.f.: A(x) = 1 + 2*x + 7*x^2 + 20*x^3 + 73*x^4 + 263*x^5 + 1111*x^6 + ...

log(A(x)) = [A(x)+1/A(-x)]*x + [A(x)^2+1/A(-x)^2]*x^2/2 + [A(x)^3+1/A(-x)^3]*x^3/3 + ...

PROG

(PARI) {a(n)=local(A=1+x+x*O(x^n)); for(i=1, n, A=exp(sum(m=1, n, (A^m+subst(A^-m, x, -x)+x*O(x^n))*x^m/m))); polcoeff(A, n)}

(PARI) {a(n)=local(A=1+x); for(i=1, n, A=(1-x*A+x*O(x^n))^-1*(1-x/subst(A, x, -x)+x*O(x^n))^-1); polcoeff(A, n)} \\ Paul D. Hanna, Dec 06 2009

CROSSREFS

Cf. A171190, A171199.

Sequence in context: A029890 A095268 A118397 * A189771 A260504 A009697

Adjacent sequences:  A171188 A171189 A171190 * A171192 A171193 A171194

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Dec 05 2009

STATUS

approved

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Last modified April 10 02:39 EDT 2020. Contains 333392 sequences. (Running on oeis4.)