2138112domain: NAppears in sequencestan(arctanh(x)*arctan(x))=2/2!*x^2+448/6!*x^6+2138112/10!*x^10...at n=2A012730G.f. satisfies: A(x) = exp( Sum_{n>=1} [Sum_{k=0..2*n} A200536(n,2*n-k)^2 * x^k] / A(x)^n * x^n/n ), where A200536(n,2*n-k) is the coefficient of x^k in (2+3*x+x^2)^n.at n=27A251689