A012838 sec(sec(x)*tanh(x))=1+1/2!*x^2+9/4!*x^4+297/6!*x^6+14385/8!*x^8...

1, 1, 9, 297, 14385, 1207729, 143876601, 23841581337, 5193194291937, 1442318342390497, 497436148816555113, 208516037618871269001, 104439610892072605613073, 61591265237655555392072593

Offset

0,3

Links

Table of n, a(n) for n=0..13.

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Sec[Sec[x]Tanh[x]], {x, 0, nn}], x] Range[0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Oct 26 2025 *)

Crossrefs

Sequence in context: A129934 A003303 A371252 * A390902 A216966 A211077

Adjacent sequences: A012835 A012836 A012837 * A012839 A012840 A012841

Keyword

nonn

Author

Patrick Demichel

Status

approved