I've noticed just recently that when I run my washer for the first time that day that there is a sewer smell n gas coming out of the drain. I am on city water, house is on slab foundation. Washer was just purchased a few months ago. After the first time the washer drains there is no smell or gases. Could someone please give advice?

Sounds like your trap is going dry. Are you draining into a floor drain or what? Traps normally have water trapped in a U shaped section, this stops sewer gas from backing into the home. https://www.google.com/search?q=how+a+floor+drain+trap+works&biw=1682&bih=835&tbm=isch&tbo=u&source=univ&sa=X&ved=0CCUQsARqFQoTCIGAoc-skMgCFQwdPgodfrsAQw