A012153 sec(tan(tan(x)))=1+1/2!*x^2+21/4!*x^4+1053/6!*x^6+96905/8!*x^8...

1, 1, 21, 1053, 96905, 14216409, 3045819741, 897606889013, 348348521840273, 172224469448231985, 105685328498514238501, 78822199814116989651661, 70223663543654715642543129, 73659278933239564262294052361

Offset

0,3

Links

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

Mathematica

With[{nn=30}, Take[CoefficientList[Series[Sec[Tan[Tan[x]]], {x, 0, nn}], x] Range[ 0, nn]!, {1, -1, 2}]] (* Harvey P. Dale, Jun 19 2021 *)

Crossrefs

Sequence in context: A263994 A072678 A218821 * A231521 A220637 A143003

Adjacent sequences: A012150 A012151 A012152 * A012154 A012155 A012156

Keyword

nonn

Author

Patrick Demichel

Status

approved