Really like that! Presumably this is because most people's sense of what feels prime is: odd numbers which don't appear in the times tables; and only 39, 51, 57

Really like that! Presumably this is because most people's sense of what feels prime is: odd numbers which don't appear in the times tables; and only 39, 51, 57, 69, 87, 91 and 93 are red herrings in that regard, all of which bar 91 are divisible by 3, which people also have a good sense of, not least by using the add the digits rule.