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The basic rule for divisibility by 4 is that if the number formed by the last two digits in a number is divisible by 4, the original number is divisible by 4; [2] [3] this is because 100 is divisible by 4 and so adding hundreds, thousands, etc. is simply adding another number that is divisible by 4. If any number ends in a two digit number that ...
206 is both a nontotient and a noncototient. [1] 206 is an untouchable number. [2] It is the lowest positive integer (when written in English as "two hundred and six") to employ all of the vowels once only, not including Y. The other numbers sharing this property are 230, 250, 260, 602, 640, 5000, 8000, 9000, 26,000, 80,000 and 90,000.
d() is the number of positive divisors of n, including 1 and n itself; σ() is the sum of the positive divisors of n, including 1 and n itselfs() is the sum of the proper divisors of n, including 1 but not n itself; that is, s(n) = σ(n) − n
For example, there are six divisors of 4; they are 1, 2, 4, −1, −2, and −4, but only the positive ones (1, 2, and 4) would usually be mentioned. 1 and −1 divide (are divisors of) every integer. Every integer (and its negation) is a divisor of itself. Integers divisible by 2 are called even, and integers not divisible by 2 are called odd.
For instance, consider division by the regular number 54 = 2 1 3 3. 54 is a divisor of 60 3, and 60 3 /54 = 4000, so dividing by 54 in sexagesimal can be accomplished by multiplying by 4000 and shifting three places. In sexagesimal 4000 = 1×3600 + 6×60 + 40×1, or (as listed by Joyce) 1:6:40.
It is an abundant number and also a superabundant number. [2] It is an idoneal number. [3] It is the least common multiple of the numbers from 1 to 8. [4] It is the smallest number divisible by every natural number from 1 to 10, except 9. It is the largest number k such that all coprime quadratic residues modulo k are squares. In this case ...
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
360 is divisible by the number of its divisors , and it is the smallest number divisible by every natural number from 1 to 10, except 7. Furthermore, one of the divisors of 360 is 72, which is the number of primes below it. 360 is the sum of twin primes (179 + 181) and the sum of four consecutive powers of three (9 + 27 + 81 + 243).