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A176025 Series reversion of eta(-x) - 1. 1
1, 1, 2, 5, 15, 49, 169, 603, 2205, 8217, 31095, 119185, 461790, 1805810, 7117865, 28250549, 112806534, 452862663, 1826705940, 7399893522, 30092189864, 122799412699, 502709227763, 2063939448400, 8496355807149, 35061664792175 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

eta(q) is the Dedekind eta function without the q^(1/24) factor (A010815).

LINKS

Table of n, a(n) for n=0..25.

FORMULA

G.f. A(x) satisfies: eta(-A(x)) = 1 + x, or, equivalently:

x = Sum_{n>=1} (-1)^[n/2]*A(x)^(n(3n-1)/2)*(1 + (-A(x))^n).

EXAMPLE

G.f.: A(x) = x + x^2 + 2*x^3 + 5*x^4 + 15*x^5 + 49*x^6 +...

eta(-x)-1 = x - x^2 - x^5 - x^7 - x^12 + x^15 + x^22 + x^26 +...

eta(-x)-1 = Sum_{n>=1} (-1)^[n/2]*x^(n(3n-1)/2)*(1 + (-x)^n).

MATHEMATICA

-InverseSeries[Series[QPochhammer[x], {x, 0, 20}]][[3]] (* Vladimir Reshetnikov, Nov 21 2015 *)

PROG

(PARI) a(n)=polcoeff(serreverse(-1+eta(-x+x*O(x^n))), n)

CROSSREFS

Cf. A010815.

Sequence in context: A149938 A148365 A001892 * A084082 A190270 A149939

Adjacent sequences:  A176022 A176023 A176024 * A176026 A176027 A176028

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Apr 06 2010

STATUS

approved

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Last modified May 26 07:30 EDT 2017. Contains 287093 sequences.