n number of observations. A single positive integer.
Else if length(n) > 1
then the length is taken to be the number required.
ndigits Number of leading digits, either 1 or 2. If 1 then the support of the distribution is {1,...,9}, else {10,...,99}.
log, log.p Logical. If log.p = TRUE then all probabilities p are given as log(p).
lower.tail Same meaning as in pnorm or qnorm.