OFFSET
0,2
LINKS
F. Heneghan and T. K. Petersen, Power series for up-down min-max permutations, 2013.
Masato Kobayashi, A new refinement of Euler numbers on counting alternating permutations, arXiv:1908.00701 [math.CO], 2019.
FORMULA
MATHEMATICA
CoefficientList[Series[Sec[x]+2Tan[x], {x, 0, 25}], x]*Table[n!, {n, 0, 25}]
PROG
(PARI) my(x='x+O('x^30)); Vec(serlaplace(1/cos(x)+2*tan(x))) \\ Michel Marcus, Aug 20 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Stefano Spezia, Aug 20 2019
STATUS
approved