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प्रश्न
For which of the numbers, from n = 2 to 8, is 2n − 1 a prime?
उत्तर
| 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.
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