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
Write all the prime numbers between:
30 and 40
Find if the following number is a prime number:
63
Express the following number as the sum of two odd prime:
36
Express the following number as the sum of two odd prime:
98
Show that the following pairs are co-primes:
161, 192
Which of the following is a prime number?
Write 'T' for true and 'F' for false for the following statement.
The sum of two odd numbers is always odd.
Write five pairs of prime numbers less than 20 whose sum is divisible by 5. (Hint : 3 + 7 = 10)
The Sum of two prime numbers is always even.
Which statement is true about composite numbers?
