Advertisements
Advertisements
Question
For which of the numbers, from n = 2 to 8, is 2n − 1 a prime?
Sum
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
Write all the prime numbers between:
30 and 40
Express the following odd number as the sum of three odd prime number:
31
State the following statement is True or False.
1 is the smallest prime number.
Show that the following pairs are co-primes:
385, 621
1 is neither ______ nor ______.
Write 'T' for true and 'F' for false for the following statement.
The sum of two even numbers is always even.
Every natural number is either prime or composite
Which of the following numbers is not a prime?
Express the following as the sum of two odd prime.
24
Which of the following number is prime?
51
