A012173 sech(tan(tanh(x)))=1-1/2!*x^2+5/4!*x^4-13/6!*x^6-1751/8!*x^8...

1, -1, 5, -13, -1751, 132871, -6935699, 5067579, 89435340497, -21076246089073, 3055142025663317, 13219661379785475, -235907327725301640967, 116095997487821991940759, -33017130566183943274793027, -532247345346868679322284213, 8810833241719412871344351850401

Offset

0,3

Links

Table of n, a(n) for n=0..16.

Mathematica

With[{nn=40}, Take[CoefficientList[Series[Sech[Tan[Tanh[x]]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Jan 15 2015 *)

Crossrefs

Sequence in context: A012032 A121228 A201260 * A009143 A240765 A127317

Adjacent sequences: A012170 A012171 A012172 * A012174 A012175 A012176

Keyword

sign

Author

Patrick Demichel (patrick.demichel(AT)hp.com)

Extensions

More terms from Harvey P. Dale, Jan 15 2015

Status

approved