I think small random uses add up to practical value although there are those who make a religion out of its 'meaning'. some (n mod 9) can be found by (is congr

I think small random uses add up to practical value although there are those who make a religion out of its 'meaning'. some (n mod 9) can be found by (is congruent to) (sum of the digits mod 9) instead is the most obvious example True only in base 10 although similar congruences exist for other bases and also involve adding the digits