# Non-Isomorphic groups of order 20 [duplicate]

How many and which distinct groups of order 20 that are not isomorphic? Why are they not isomorphic? I have the $Z_{20}, Z_2+Z_{10}, D_{10}$.
• There are exactly $5$ non-isomorphic groups of order $20$. If you are aware of semi-direct products, look at SnowAngel6147's answer in the link Dan provided. If you know about presentations, the remaining two can also be found here and here. – NotAwake Nov 29 '13 at 6:38