Surprising that the author finds it surprising. In base-10 it's as easy as "a number is divisible by 3 or 9* iff sum of its digits is divisible", which is trivially independent of endiannes and slightly less trivial, but still possible, to check in O(1) extra space.
Surprising that the author finds it surprising. In base-10 it's as easy as "a number is divisible by 3 or 9* iff sum of its digits is divisible", which is trivially independent of endiannes and slightly less trivial, but still possible, to check in O(1) extra space.
* s/6/9/ Typo, thanks apothegm.
True of 9 but not of 6 (trivial example of the latter: 36).