"Welcome Back Kotter" was originally going to be called simply "Kotter", but that was changed because John Sebastian, who once fronted the Lovin' Spoonful, failed to find any relevant words that rhymed with Kotter.

http://goretro.blogspot.com/search/label/TV%20show%20themes

That was a fun article. I love TV theme songs so it's fun to read the stories behind them. I think "Welcome Back Kotter" is a better title than "Kotter" anyway. And it's a great theme song too!