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If the hundreds digit is even, the number formed by the last two digits must be divisible by 8. 624: 24. If the hundreds digit is odd, the number obtained by the last two digits must be 4 times an odd number. 352: 52 = 4 × 13. Add the last digit to twice the rest. The result must be divisible by 8. 56: (5 × 2) + 6 = 16.
The tables below list all of the divisors of the numbers 1 to 1000. A divisor of an integer n is an integer m , for which n / m is again an integer (which is necessarily also a divisor of n ). For example, 3 is a divisor of 21, since 21/7 = 3 (and therefore 7 is also a divisor of 21).
In mathematics, a square-free integer (or squarefree integer) is an integer which is divisible by no square number other than 1. That is, its prime factorization has exactly one factor for each prime that appears in it. For example, 10 = 2 ⋅ 5 is square-free, but 18 = 2 ⋅ 3 ⋅ 3 is not, because 18 is divisible by 9 = 3 2. The smallest ...
128 is the seventh power of 2. It is the largest number which cannot be expressed as the sum of any number of distinct squares. [1] [2] However, it is divisible by the total number of its divisors, making it a refactorable number. [3] The sum of Euler's totient function φ(x) over the first twenty integers is 128. [4]
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 children's teaching materials including higher multiples such as "quadruply even." [3]
Formally, a regular number is an integer of the form , for nonnegative integers , , and .Such a number is a divisor of (⌈ / ⌉,,).The regular numbers are also called 5-smooth, indicating that their greatest prime factor is at most 5. [2]
The number 18 is a harshad number in base 10, because the sum of the digits 1 and 8 is 9, and 18 is divisible by 9.; The Hardy–Ramanujan number (1729) is a harshad number in base 10, since it is divisible by 19, the sum of its digits (1729 = 19 × 91).
An extravagant number has fewer digits than its prime factorization. The first in decimal: 4, 6, 8, 9, 12, 18, 20, 22, 24, 26, 28, 30 (sequence A046760 in the OEIS). An economical number has been defined as a frugal number, but also as a number that is either frugal or equidigital.