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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.
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 number's being divisible by 4 is sufficient (but not necessary) for it to be even, but being divisible by 2 is both sufficient and necessary for it to be even. Example 3 An occurrence of thunder is a sufficient condition for the occurrence of lightning in the sense that hearing thunder, and unambiguously recognizing it as such, justifies ...
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 ...
As another example, φ(1) = 1 since for n = 1 the only integer in the range from 1 to n is 1 itself, and gcd(1, 1) = 1. Euler's totient function is a multiplicative function , meaning that if two numbers m and n are relatively prime, then φ ( mn ) = φ ( m ) φ ( n ) .
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]