Dear friends, I installed the package “uroot” then I wrote library (uroot) and I entered a series entitled extp, in spite of that the problem persite. In short,here are what I wrote and the message that I obtained: 
> library(uroot)
> extp=c(1,3,10,14,12,5,8,12,13,15,9,8,7,10,9,7,3,10,3,11,12,7,4,9,8,10,20,17)
> CH.test (wts=extp, frec=c(1,1), f0=1, DetTr=FALSE, ltrunc=NULL)
Erreur dans seq.default(2, qq * 2, 2) : signe incorrect de l'argument 'by'

The last line wants to say that there is incorrect sign of the argument “by”
Which will be your suggestions, thank you.
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