▲ 1265 ▼ Panik (i.postimg.cc) submitted 2 years ago by ickplant@lemmy.world to c/lemmyshitpost@lemmy.world 146 comments fedilink hide all child comments
[–] Tangent5280@lemmy.world 35 points 2 years ago (1 child) Our plan to find the witch has worked, boys! Get her! permalink fedilink source parent hideshow 2 child comments replies: [–] Karyoplasma@discuss.tchncs.de 3 points 2 years ago For divisibility by 13, take the last number, multiply by 4 and add to the rest. For divisibility by 17, take the last number, multiply by 5 and subtract from the rest. For divisibility by 19, take the last number, multiply by 2 and add to the rest. In fact, you can adapt the method to check for divisibility by any prime number k. permalink fedilink source parent
[–] Karyoplasma@discuss.tchncs.de 3 points 2 years ago For divisibility by 13, take the last number, multiply by 4 and add to the rest. For divisibility by 17, take the last number, multiply by 5 and subtract from the rest. For divisibility by 19, take the last number, multiply by 2 and add to the rest. In fact, you can adapt the method to check for divisibility by any prime number k. permalink fedilink source parent
