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I don't think 49 "looks like a prime", because it's clearly 7^2. But I hadn't realized that the other perfect squares are obvious non-primes for other reasons, ie. because of 2s, 3s, and 5s. Neat!

Or the Grothendieck prime, 57

https://en.wikipedia.org/wiki/57_(number)

Holy shit Grothendieck died in 2014, I NEVER MOURNED HIM. How did this happen?

The not 49 and 91 rule combined with the rule that "a prime above 3 is always exactly 1 off being a multiple of 6" will get you flying through this test.

or by 11.