People suffering this fear would goshly stay off on an airplane that is numbered 191, as well as not being in a non-airplane vehicle numbered 191, such as that said on a license plate. In fact, the Listverse webpage lists 191 as the unluckiest number. They may think the superstition of number 191 goes beyond aviation and is therefore the number is unlucky. The fear of the number came about due to numerous airplane crashes that has flight number 191, though the fear may not be as numerous as it was because Flight numbered 191 was abandoned by American and Delta Airlines. Fear of the number has close ties with fear of number 11 because the sum of digits in 191 is 11, as well as fear of number 911 by simply rearranging them. This method works on the idea of sifting the composite numbers to identify the prime numbers.Hekatenenekontahenophobia (from Greek hekato, "one hundred", enenekonta, "ninety", and hen, "one") is the fear of the number 191.
Finding Prime Numbers Using Sieve of EratosthenesĪn interesting way of finding prime numbers is by using the Sieve of Eratosthenes. Now, the last digit of 37 is neither 0 nor 5, so it’s not divisible by 5 as well.Īs 37 cannot have any factor greater than 6, we can stop with 6. Next, the sum of the digits of 37 is: 3 + 7 = 10. Subsequently, 37 is not divisible by 4, 6, or 8. Let’s perform the divisibility tests one by one.ģ7 is not an even number, so it’s not divisible by 2. Now, the divisibility test for 3 is to check if the sum of the digits is divisible by 3. So, we’ll bring the divisibility rules into play.Ģ67 is not an even number, so it’s not divisible by 2. Listing the factors of this number would be time-consuming. The quickest way of finding the factors of larger numbers, though, is by using the divisibility rules. The number 13 has only two divisors of 1,13. The number 0 is not a prime number - it is not a positive number and has infinite number of divisors. So with small numbers, your job of telling whether a number is prime or composite is super-easy. The number 1 is not a prime number by definition - it has only one divisor. So, 5 is a prime number.Ħ = 1 x 6 6 = 2 x 3. So, it is a prime number.Ĥ = 1 x 4 4 = 2 x 2. So, it is neither prime nor composite.Ģ = 1 x 2. Let’s take a look at the first few prime numbers.ġ = 1 x 1.
A number that has only two factors, 1 and the number itself, is called a prime number.Ī number that has more than two factors is called a composite number.
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