Prime Safari

1 lurker | 18 watchers

fetcheveryone Dec 2024 10:22am, 21 Dec 2024 31,421 posts	0 fetcheveryone Struck lucky in the parkrun lottery.
Jigs Dec 2024 12:51pm, 21 Dec 2024 14,519 posts	0 Jigs
In the bleak midWinniefree Dec 2024 12:52pm, 21 Dec 2024 9,028 posts	0 In the bleak midWinniefree A little trick if you need one, apparently if you add the digits of any number together and it is divisible by 3 it’s not a prime number.
um Dec 2024 1:05pm, 21 Dec 2024 9,133 posts	0 um If my earlier ones were dodgy and risk of being judged cheating because they were not 'out in the wild', here's one from the wild, almost exactly at the 700 mile point. Unfortunately there wasn't a bin. closer up The emergency number, not the excavation one!
um Dec 2024 1:06pm, 21 Dec 2024 9,134 posts	0 um The first ic was meant to be this one!
In the bleak midWinniefree Dec 2024 1:06pm, 21 Dec 2024 9,031 posts	0 In the bleak midWinniefree Although it just tried it with 20 and that clearly doesn’t work! As you were.
um Dec 2024 1:15pm, 21 Dec 2024 9,136 posts	0 um If the sum of the digits is divisible by 3, it means the number is divisible by three, therefore not prime. You can rule out anything ending in 0, 2, 4, 6 or 8 as well (divisible by 2) and anything ending in 5.
Derek Dec 2024 1:16pm, 21 Dec 2024 First-time poster!!	0 Derek Great read
Turkey 🐔 Giblets Dec 2024 1:19pm, 21 Dec 2024 264 posts	0 Turkey 🐔 Giblets Useful webpage
Turkey 🐔 Giblets Dec 2024 1:20pm, 21 Dec 2024 265 posts	0 Turkey 🐔 Giblets (helps if I add the link) numberempire.com