Advertisements
Advertisements
Question
For which of the numbers, from n = 2 to 8, is 2n − 1 a prime?
Sum
Advertisements
Solution
| n | 2n − 1 | Result | Prime/Not Prime |
| 2 | 2 × 2 − 1 = 4 − 1 | 3 | Prime |
| 3 | 2 × 3 − 1 = 6 − 1 | 5 | Prime |
| 4 | 2 × 4 − 1 = 8 − 1 | 7 | Prime |
| 5 | 2 × 5 − 1 = 10 − 1 | 9 | Not prime |
| 6 | 2 × 6 − 1 = 12 − 1 | 11 | Prime |
| 7 | 2 × 7 − 1 = 14 − 1 | 13 | Prime |
| 8 | 2 × 8 − 1 = 16 − 1 | 15 | Not prime |
For n = 2, 3, 4, 6 and 7 it is prime.
shaalaa.com
Is there an error in this question or solution?
APPEARS IN
RELATED QUESTIONS
Give examples of five pairs of co-primes.
State the following statement is True or False.
The sum of two prime numbers is always a prime number.
Show that the following pairs are co-primes:
512, 945
Find the HCF of
Two prime numbers
Which of the following is a prime number?
Write all prime numbers between 50 and 100.
Write the smallest and the biggest two digit prime number
The digits of the prime number 13 can be reversed to get another prime number 31. Find if any such pairs exist upto 100
Express the following as the sum of two odd prime.
24
The Sum of two prime numbers is always even.
