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 A191003 E.g.f. arctan(x/cos(x)) (odd powers only). 4
 1, 1, -11, -83, 6921, 60281, -29132611, 208438245, 427918448785, -22588439158415, -15853957892902395, 2325342085659612317, 1210510298677225936025, -389238357419648883489303, -164119044571112073285613619 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA a(n)=(2*n+1)!*(2*sum(m=0..n-1, ((-1)^(m)*sum(j=0..(n-m), binomial(m+j-1/2,j)*4^(n-m-j)*sum(i=0..j, (i-j)^(2*n-2*m)*binomial(2*j,i)*(-1)^(n-m+j-i))))/((2*m+1)*(2*n+1-2*m-1)!))+(-1)^(n)/(2*n+1)). EXAMPLE arctan(x/cos(x)) = x + 1/6*x^3 - 11/120*x^5 - 83/5040*x^7 +- ... MATHEMATICA With[{nn=30}, Take[CoefficientList[Series[ArcTan[x/Cos[x]], {x, 0, nn}], x] Range[0, nn-1]!, {2, -1, 2}]] (* Harvey P. Dale, May 28 2014 *) PROG (Maxima) a(n):=(2*n+1)!*(2*sum(((-1)^(m)*sum(binomial(m+j-1/2, j)*4^(n-m-j)*sum((i-j)^(2*n-2*m)*binomial(2*j, i)*(-1)^(n-m+j-i), i, 0, j), j, 0, (n-m)))/((2*m+1)*(2*n+1-2*m-1)!), m, 0, n-1)+(-1)^(n)/(2*n+1)); CROSSREFS Sequence in context: A167577 A129077 A152582 * A012478 A239461 A330966 Adjacent sequences:  A191000 A191001 A191002 * A191004 A191005 A191006 KEYWORD sign AUTHOR Vladimir Kruchinin, Jun 16 2011 STATUS approved

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Last modified June 17 13:12 EDT 2021. Contains 345080 sequences. (Running on oeis4.)