Aeschylus, Prometheus Bound 459-461
Prometheus takes credit for giving humans numbers and letters.
καὶ μὴν ἀριθμόν, ἔξοχον σοφισμάτων,
ἐξηῦρον αὐτοῖς, γραμμάτων τε συνθέσεις
μνήμην ἁπάντων, μουσομήτορ’ ἐργάνην.
And indeed for their benefit I found out number, an exceptional thing among ingenious devices; and the combination of letters as a memory of all things, the hard-working mother of the Muses.