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Its a weird thing where in smaller scales, primes numbers that LOOK prime are decent candidates of actually being prime.
by NikolaeVarius 5y ago
Its a weird thing where in smaller scales, primes numbers that LOOK prime are decent candidates of actually being prime.
- madcaptenor 5y agoAll one- and two-digit numbers that look prime are prime, except 91. This assumes that you can easily identify - multiples of 2 and 5 (by their last digit) - multiples of 3 (the sum of their digits is divisible by 3) - multiples of 11 (for two-digit ones, they have both digits the same: 11, 22, 33, ..., 99) - squares So the first number that looks prime but isn't is the product of the two smallest primes that aren't "easy", which is 7*13 = 91.