21751554825domain: NAppears in sequencesDenominators of coefficients of expansion of arctan(x)^2 = x^2-2/3*x^4+23/45*x^6-44/105*x^8+563/1575*x^10-3254/10395*x^12+ ...at n=13A071968a(n) = A392686(n)/2.at n=6A390227