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 A235166 E.g.f. satisfies: A'(x) = A(x)^2/A(-x)^2, with A(0)=1. 2
 1, 1, 4, 16, 88, 640, 5440, 54400, 620800, 7966720, 113651200, 1783091200, 30519808000, 565916876800, 11300689100800, 241781039104000, 5517822373888000, 133795711025152000, 3435107208822784000, 93093522064998400000, 2655675672405606400000, 79546285618254315520000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS See comments by Roland Bacher in A098777 which imply that this sequence is related to elliptic functions. Compare to: G'(x) = G(x)^2/G(-x) dx, which holds when G(x) = 1/(cos(x) - sin(x)), the e.g.f. of A001586 (Springer numbers). LINKS Paul D. Hanna and Vaclav Kotesovec, Table of n, a(n) for n = 0..200 (first 100 terms from Paul D. Hanna) FORMULA E.g.f.: 1/(1 - 3*Series_Reversion( Integral 1/(1 - 9*x^2)^(2/3) dx ))^(1/3). E.g.f.: 1/F(x), where F(x) equals the e.g.f. of A098777 (pseudo-factorials). a(n) ~ 2^(-2/3) * n! * (9*GAMMA(2/3)^3/(2^(2/3)*Pi^2))^(n+1). - Vaclav Kotesovec, Feb 24 2014 EXAMPLE E.g.f.: A(x) = 1 + x + 4*x^2/2! + 16*x^3/3! + 88*x^4/4! + 640*x^5/5! +... Related series. A(x)^2 = 1 + 2*x + 10*x^2/2! + 56*x^3/3! + 400*x^4/4! + 3440*x^5/5! +... 1/A(x) = 1 - x - 2*x^2/2! + 2*x^3/3! + 16*x^4/4! - 40*x^5/5! - 320*x^6/6! +...+ A098777(n)*x^n/n! +... MATHEMATICA kmax = 21; A[x_] = 1+x; Do[A[x_] = 1+Integrate[A[x]^2/A[-x]^2+O[x]^k, x] // Normal, {k, 1, kmax}]; CoefficientList[A[x], x] Range[0, kmax]! (* Jean-François Alcover, Jul 29 2018 *) PROG (PARI) {a(n)=local(A=1+x); for(i=0, n, A=1+intformal(A^2/subst(A, x, -x +x*O(x^n))^2 +x*O(x^n) )); n!*polcoeff(A, n)} for(n=0, 21, print1(a(n), ", ")) (PARI) {a(n)=local(A=1); A=1/(1-3*serreverse(intformal(1/(1-9*x^2 +x*O(x^n))^(2/3))))^(1/3); n!*polcoeff(A, n)} for(n=0, 20, print1(a(n), ", ")) CROSSREFS Cf. A001586, A098777. Sequence in context: A005618 A005495 A052124 * A013030 A124962 A292088 Adjacent sequences:  A235163 A235164 A235165 * A235167 A235168 A235169 KEYWORD nonn AUTHOR Paul D. Hanna, Jan 04 2014 STATUS approved

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Last modified June 24 10:36 EDT 2021. Contains 345416 sequences. (Running on oeis4.)