What is the name of the Brady Bunch episode where Peter Brady tickles Bobby Brady half to death and why did Peter tickle his brother in the first place?

I think it's "Will the Real Jan Brady Please Stand Up?" It was the one where Jan gets a wig to stand out from the crowd. Peter is tickling Bobby to make him tell who's going to be at Lucy Winters' birthday party. When Bobby can't take it anymore he screams "Maaaaargie....Margie Whipple."