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A013338 Expansion of e.g.f.: sec(exp(x)-sec(x))=1+1/2!*x^2+9/4!*x^4-20/5!*x^5+177/6!*x^6... 0
1, 0, 1, 0, 9, -20, 177, -1260, 7105, -99144, 564049, -10278840, 77134761, -1412196188, 15082747617, -257693157540, 3771722331457, -62330454304272, 1150241027577697, -19671866661968880, 420212562193269513 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,5

LINKS

Table of n, a(n) for n=0..20.

MATHEMATICA

With[{nn=20}, CoefficientList[Series[Sec[Exp[x]-Sec[x]], {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Feb 19 2020 *)

CROSSREFS

Sequence in context: A230833 A321723 A282763 * A008847 A143243 A157812

Adjacent sequences:  A013335 A013336 A013337 * A013339 A013340 A013341

KEYWORD

sign

AUTHOR

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

EXTENSIONS

Definition clarified by Harvey P. Dale, Feb 19 2020

STATUS

approved

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Last modified June 19 03:36 EDT 2021. Contains 345125 sequences. (Running on oeis4.)