108113domain: NAppears in sequencessec(sec(x)*arctanh(x))=1+1/2!*x^2+25/4!*x^4+1225/6!*x^6+108113/8!*x^8...at n=4A012851Numbers k such that the continued fraction for sqrt(k) has odd period and if the last term of the periodic part is deleted the two central terms are both 28.at n=17A031616