%I #7 Feb 24 2012 12:51:04
%S 2,-128,253952,-2863136768,107451055603712,-10140668012798148608,
%T 2022780765718183801782272,-757569427466144902069404827648
%N arctan(tanh(x)*tan(x))=2/2!*x^2-128/6!*x^6+253952/10!*x^10...
%F (-1)^n * 2^(6n+1) * A090681(n).
%K sign
%O 0,1
%A Patrick Demichel (patrick.demichel(AT)hp.com)
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