sech(arctan(tanh(x)))=1-1/2!*x^2+21/4!*x^4-1101/6!*x^6+109001/8!*x^8...

A012230

sech(arctan(tanh(x)))=1-1/2!*x^2+21/4!*x^4-1101/6!*x^6+109001/8!*x^8...

Terms

    a(0) =1a(1) =-1a(2) =21a(3) =-1101a(4) =109001a(5) =-17491001a(6) =4139085981

External references