It is probable an error in your question.The meaning of Nr. is number.
The mathematical term for "mean" is "mean".The popular, or colloquial term for "mean" is "average".
"plus" It usually indicates addition.
The entire group being studied.
A number that has a multiplicative inverse. That is, x is a unit iff there exists some y such that x*y = y*x = 1.
not reallyy ;) ;) ;)
Depending on the context -- the sentence or phrase where NR is used -- it may mean 'natural round'.
New relationship status ?
NR stands for the designers Nancy & Rise, New York 1987