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Take each digit of the number (371) in reverse order (173), multiplying them successively by the digits 1, 3, 2, 6, 4, 5, repeating with this sequence of multipliers as long as necessary (1, 3, 2, 6, 4, 5, 1, 3, 2, 6, 4, 5, ...), and adding the products (1×1 + 7×3 + 3×2 = 1 + 21 + 6 = 28). The original number is divisible by 7 if and only if ...
Furthermore, if b 1, b 2 are both coprime with a, then so is their product b 1 b 2 (i.e., modulo a it is a product of invertible elements, and therefore invertible); [6] this also follows from the first point by Euclid's lemma, which states that if a prime number p divides a product bc, then p divides at least one of the factors b, c.
Zelinsky proved that no three consecutive integers can all be refactorable. [1] Colton proved that no refactorable number is perfect . The equation gcd ( n , x ) = τ ( n ) {\displaystyle \gcd(n,x)=\tau (n)} has solutions only if n {\displaystyle n} is a refactorable number, where gcd {\displaystyle \gcd } is the greatest common divisor function.
t(n) = C(n + 1, 2) = n(n + 1) / 2 = 1 + 2 + ... + n for n ≥ 1, with t(0) = 0 (empty sum). A000217: Square numbers n 2: 0, 1, 4, 9, 16, 25, 36, 49, 64, 81, ... n 2 = n × n: A000290: Tetrahedral numbers T(n) 0, 1, 4, 10, 20, 35, 56, 84, 120, 165, ... T(n) is the sum of the first n triangular numbers, with T(0) = 0 (empty sum). A000292 ...
a prime number has only 1 and itself as divisors; that is, d(n) = 2 a composite number has more than just 1 and itself as divisors; that is, d ( n ) > 2 a highly composite number has a number of positive divisors that is greater than any lesser number; that is, d ( n ) > d ( m ) for every positive integer m < n .
Singly even numbers are those with ν 2 (n) = 1, i.e., integers of the form 4m + 2. Doubly even numbers are those with ν 2 (n) > 1, i.e., integers of the form 4m. In this terminology, a doubly even number may or may not be divisible by 8, so there is no particular terminology for "triply even" numbers in pure math, although it is used in ...
This upcoming stretch could bring 1 to 2 feet of snow to the city, depending on each storm’s ultimate track. A similar scenario could unfold in New York City. Less than 10 inches of snow ...
Cuisenaire rods: 5 (yellow) cannot be evenly divided in 2 (red) by any 2 rods of the same color/length, while 6 (dark green) can be evenly divided in 2 by 3 (lime green). In mathematics, parity is the property of an integer of whether it is even or odd. An integer is even if it is divisible by 2, and odd if it is not. [1]