The divisibility test that an integer is divisible
by 9 iff the sum of its digits is divisible by 9.
See alsoCasting Out Nines
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ReferencesFlannery, S. and Flannery, D. In Code: A Mathematical Journey. London: Profile Books, pp. 115-116, 2000.
on Wolfram|AlphaRule of Nines
Cite this as:
Weisstein, Eric W. "Rule of Nines." From
MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/RuleofNines.html