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Subtract the last two digits from four times the rest. The result must be divisible by 13. 923: 9 × 4 − 23 = 13. Subtract 9 times the last digit from the rest. The result must be divisible by 13. (Works because 91 is divisible by 13). 637: 63 − 7 × 9 = 0. 14: It is divisible by 2 and by 7. [6] 224: it is divisible by 2 and by 7.
Demonstration, with Cuisenaire rods, that 1, 2, 8, 9, and 12 are refactorable. A refactorable number or tau number is an integer n that is divisible by the count of its divisors, or to put it algebraically, n is such that (). The first few refactorable numbers are listed in (sequence A033950 in the OEIS) as
The digit sum of 2946, for example is 2 + 9 + 4 + 6 = 21. Since 21 = 2946 − 325 × 9, the effect of taking the digit sum of 2946 is to "cast out" 325 lots of 9 from it. If the digit 9 is ignored when summing the digits, the effect is to "cast out" one more 9 to give the result 12.
Digit sums and digital roots can be used for quick divisibility tests: a natural number is divisible by 3 or 9 if and only if its digit sum (or digital root) is divisible by 3 or 9, respectively. For divisibility by 9, this test is called the rule of nines and is the basis of the casting out nines technique for checking calculations.
12 (twelve) is the natural number following 11 and preceding 13.. Twelve is the 3rd superior highly composite number, [1] the 3rd colossally abundant number, [2] the 5th highly composite number, and is divisible by the numbers from 1 to 4, and 6, a large number of divisors comparatively.
On Dec. 9, Carter’s attorney Spiro, who got Alec Baldwin’s involuntary manslaughter case dismissed in July, filed a motion denying Doe’s request to proceed without being publicly named or to ...
DETROIT (Reuters) -U.S. automakers Ford Motor and General Motors will donate $1 million each, along with vehicles, to U.S. President-elect Donald Trump's January inauguration, company ...
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