sech(arctan(arctanh(x)))=1-1/2!*x^2+5/4!*x^4-109/6!*x^6+2729/8!*x^8...

A012239

sech(arctan(arctanh(x)))=1-1/2!*x^2+5/4!*x^4-109/6!*x^6+2729/8!*x^8...

Terms

    a(0) =1a(1) =-1a(2) =5a(3) =-109a(4) =2729a(5) =-196281a(6) =9832173a(7) =-1827291621a(8) =102520239057

External references