Exponent (p)

Primes

$2^{p-3}$ exponent

$2^{p-3}-1$

$\left(2^{p-3}-1\right)/3$

Group

2

3

3

7

0

5

31

2

1

7

127

4

15

5

2

13

8,191

10

1,023

341

2

17

131,071

14

16,383

5,461

2

19

524,287

16

65,535

21,845

2

31

2,147,483,647

28

268,435,455

89,478,485

2