A003700 Expansion of tan(x /cosh(x)).

1, -1, -19, 475, 1753, -1109769, 70784325, 2711086547, -1376283649103, 148592152807663, 21812320857733789, -12754009647903010101, 1675171082535404962441, 847081835857552788679655

Offset: 0

Author

R. H. Hardin, N. J. A. Sloane, Simon Plouffe

Keywords

• sign

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Programs

Mathematica

Tan[ x/Cosh[ x ] ] (* Odd Part *)
nn = 20; Table[(CoefficientList[Series[Tan[x*Sech[x]], {x, 0, 2*nn+1}], x] * Range[0, 2*nn+1]!)[[n]], {n, 2, 2*nn, 2}] (* Vaclav Kotesovec, Feb 16 2015 *)