1 min and 35 seconds left
AWESOME. LOL
211 is prime. This also works with 27 since 2+7 sums to a multiple of 3. 277 and 271 are prime.
Other first two digits follow a pattern. 127 151 157 181 211 241 271 are prime.
If three digits sum to a multiple of 3 the number is not prime. 111 117 171 177 207. Divide these numbers by three as a proof.
Of course some memorize. Let me know how You memorize prime numbers, please.
1 min and 35 seconds left
AWESOME. LOL
211 is prime. This also works with 27 since 2+7 sums to a multiple of 3. 277 and 271 are prime.
Other first two digits follow a pattern. 127 151 157 181 211 241 271 are prime.
If three digits sum to a multiple of 3 the number is not prime. 111 117 171 177 207. Divide these numbers by three as a proof.
Of course some memorize. Let me know how You memorize prime numbers, please.