Medication identification....viagra? illegal drug?

I have found some pills that my boyfriend has, loose in a plastic bag and I am desperatley needing to know what they are. They are a mixture of bright blue and red. The red ones are 3 sided with smooth edges and have either OS or 20 imprinted on them....I thought it was OS but now thinking about it read the other way could be 20! I have found regular sidenafil...prescribed before but never these loose in a plastic bag...around 20 of them. I just wondered with the description of the red ones if anyone knows what they could be?