The integrals below involve `sech ax`.
1) `int sech ax dx = 2/a tan^-1 e^(ax)`
2) `int sech^2 ax dx = (tanh ax)/a`
3) `int sech^3 ax dx = (sech ax*tanh ax)/(2a)+1/(2a) tan^-1 sinh ax`
4) `int sech^n ax*tanh ax dx = -(sech^n ax)/(na)`
5) `int 1/(sech ax) dx = (sinh ax)/a`
6) `int x sech ax dx = 1/a^2{(ax)^2/2-(ax)^4/8+(5(ax)^6)/144+...((-1)^nE_n(ax)^(2n+2))/((2n+2)(2n)!)+...}`
7) `int x sech^2 ax dx = (x tanh ax)/a-1/a^2 ln cosh ax`
8) `int (sech ax)/x dx = ln x-(ax)^2/4+(5(ax)^4)/96-(61(ax)^6)/4320+...((-1)^nE_n(ax)^(2n))/(2n(2n)!)+...`
9) `int 1/(q+p sech ax) dx = x/q-p/q int 1/(p+q cosh ax) dx`
**[See integral #20 in the table involving `cosh ax`]
10) `int sech^n ax dx = (sech^(n-2) ax tanh ax)/(a(n-1))+(n-2)/(n-1) int sech^(n-2) ax dx`