F3

F3, F3 or f3 may refer to:
* F3 = 2 (F stands for s)
* 0xF3 = 243
* F3 = 257, the second largest known Fermat prime
* Trialogue (F3 in PsiCubed2's Letter Notation)
* f3 in the fast-growing hierarchy (approximately tetrational growth rate)