what is the meaning of this expression ?

zetafunction

where / means a quotient group

if n=1 then is the set of integers modulus n {0,1,2,3,4,....,n-1} in case

m=2 we have a binary system, but i do not know what (1) will mean

of ocurse 'Z' means the set of all (positive) integers.

matt grime

What is (1)?

Anyway, this only makes sense if n divides m as you need mZ to be a subgroup of nZ.

In this case you can just factor n out and be left with something isomorphic to Z/m'Z where m=nm'.

They are not equal - the the cosets are different but they are isomorphic.