Sorry for the simple question, but I last took Latin in 1987 and I don't remember how to make a first-person plural imperative for "cogitare" (or any "are" verbs), and my Google searches are failing me. I've found many sites that conjugate "cogitare" and/or "are" verbs, but they only include the four "standard" imperatives: active singular (cogita), active plural (cogitate), passive singular (cogitare) and passive plural (cogitamini), but I'm pretty sure they are all second person (you) as far as I can tell.
This all started trying to translate "let's think!" or "let's think together!" into Latin for a motto.