From this, we can also say that we can avoid the numbers ending in 0, 2, 4, 6 and 8 or even numbers in general as they will have factors. So, for a given number n, one should check for the factors up to \ value. Note: Generally, students miss out factors while finding whether a number is prime or composite. For example, here are two ways to list the first 100 primes: require 'mathn' list gen Prime.new gen.each do prime list << prime break if list.size. The pairs except 13 and 31 are 17 and 71, 37 and 73. That is, if a number is not divisible by anything except 1 and the number itself, then it is called a prime number. Now, let's consider examples like 5, its factors are only 1 and 5, so, it’s a prime number, while, for 4 it's factors are 1 and 4 as well as 2. Every natural number has both 1 and itself as a divisor and if a number has no divisor other than 1 and itself it is considered as prime otherwise, it is considered as composite. The first abundant numbers are: 1 (1 divisor ), 2 (2 divisors ), 4 (3. The divisors of natural number n are the natural number that divides n evenly. What is the list of divisors from 1 to 100. In the question, we are said that both 13 and 31 prime numbers and both these numbers have the same digits 1 and 3 and thus, we have to find such pairs.īefore proceeding let us know about some information. Hint: At first, collect and write all the numbers between 1 to 100 and then we observe one by one and see that there are a total of three pairs just like the pair 13 and 31.
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