how the temperature is inversilyproportional to nmber of molecules

it can seen from ideal gas equation that 

taking P and V as constant then  Tn = constant 

in understanding or theoritical way of understanding it is when we heat up a gas taking it’s volume and pressure constant which can be done by taking an open system an if we take a closed system it’s pressure will increase and not become constant so we take an open system when we heat gas, gas moleule moves out of the container and number of moles of gas increases.