Comment on And 299999999 is divisible by 13
OfficerBribe@lemm.ee 2 weeks ago
Never realized there are so many rules for divisibility. This post fits in this category:
Forming an alternating sum of blocks of three from right to left gives a multiple of 7
299,999 would be 999 - 299 = 700 which is divisible by 7. And if we simply swap grouped digits to 999,299, it is also divisible by 7 since 299 - 999 = -700.
grubberfly@mander.xyz 2 weeks ago
That is indeed an absurd amount of rules (specially for 7) !
It should be fun to develop each proof. Specially the 1,3,2,-1,-3,-2 rule