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 A012101 Expansion of tan(arcsin(sinh(x))) (odd powers only). 2
 1, 4, 76, 3424, 277456, 35345344, 6504742336, 1632531979264, 535821754153216, 222769351470429184, 114411762387714436096, 71132353206363509039104, 52648938670226334981246976 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS G. C. Greubel, Table of n, a(n) for n = 0..219 FORMULA a(n) = Sum_{m=0..n} ( binomial(2*m,m)*2^(-4*m)*( Sum_{i=0,..,(2*m+1)/2} (2*i-2*m-1)^(2*n+1)*binomial(2*m+1,i)*(-1)^(i+1) ) ). - Vladimir Kruchinin, Jun 15 2011 E.g.f.: sinh(x) / sqrt(1 - sinh(x)^2). - Vaclav Kotesovec, Feb 06 2015 a(n) ~ (2*n+1)! / (sqrt(Pi*n) * 2^(1/4) * (log(1+sqrt(2)))^(2*n+3/2)). - Vaclav Kotesovec, Feb 06 2015 EXAMPLE tan(arcsin(sinh(x))) = x+4/3!*x^3+76/5!*x^5+3424/7!*x^7+277456/9!*x^9... MATHEMATICA nn = 20; Table[(CoefficientList[Series[Sinh[x]/Sqrt[1 - Sinh[x]^2], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* Vaclav Kotesovec, Feb 06 2015 *) Table[Sum[Binomial[2*m, m]*2^(-4*m)*Sum[(2*i - 2*m - 1)^(2*n + 1)* Binomial[2*m + 1, i]*(-1)^(i + 1), {i, 0, (2*m + 1)/2}], {m, 0, n}], {n, 0, 50}] (* G. C. Greubel, Feb 15 2017 *) PROG (Maxima) a(n):=sum(binomial(2*m, m)*2^(-4*m)*sum((2*i-2*m-1)^(2*n+1)*binomial(2*m+1, i)*(-1)^(i+1), i, 0, (2*m+1)/2), m, 0, n); /* Vladimir Kruchinin, Jun 15 2011 */ CROSSREFS Cf. A012571. Sequence in context: A012020 A012041 A024258 * A012080 A012047 A012010 Adjacent sequences: A012098 A012099 A012100 * A012102 A012103 A012104 KEYWORD nonn AUTHOR Patrick Demichel (patrick.demichel(AT)hp.com) EXTENSIONS Typo in second formula corrected (following a suggestion of Sergei N. Gladkovskii) by Vaclav Kotesovec, Apr 17 2017 STATUS approved

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Last modified March 25 23:39 EDT 2023. Contains 361529 sequences. (Running on oeis4.)