Posts by opal@ioc.exchange
 (DIR) Post #AXY911syeDHIGAZylc by opal@ioc.exchange
       2023-07-10T11:22:59Z
       
       0 likes, 0 repeats
       
       @grammargirl Even cooler: this pattern applies to other number systems (bases), too!One other fun thing: you can use this rule to check if a number is divisble by 9. Just add up the digits, and see if it's divisible by 9.For instance: 3312 is divisible by 9 because 3+3+1+2=9. 5166 is divisible by 9 because 5+1+6+6=18, and 1+8=9.It's a really cool rule!
       
 (DIR) Post #AZy97w0oUsnuCzBuJE by opal@ioc.exchange
       2023-09-20T16:24:27Z
       
       2 likes, 0 repeats
       
       @ian 8675309 (as in, Jenny's number from the Tommy Tutone song) is a prime number. What's more, it's the bottom half of a twin prime pair: add 2, and you get 8675311, which is ALSO prime.If you're writing software that implements number-theoretic algorithms, it can be problematic to test it using small primes like 7 or 11, because small primes tend to have a lot of weird properties tend to trigger exceptions and edge cases. Having a pair of easy-to-remember, "big enough" prime numbers like the Jenny primes is really useful.