A064078 - cp's OEIS frontend

A064078 Zsigmondy numbers for a = 2, b = 1: Zs(n, 2, 1) is the greatest divisor of 2^n - 1 (A000225) that is coprime to 2^m - 1 for all positive integers m < n.

n	a(n)
1	1
2	3
3	7
4	5
5	31
6	1
7	127
8	17
9	73
10	11
11	2047
12	13
13	8191
14	43
15	151
16	257
17	131071
18	19
19	524287
20	41
21	337
22	683
23	8388607
24	241
25	1082401
26	2731
27	262657
28	3277
29	536870911
30	331
31	2147483647
32	65537
33	599479
34	43691
35	8727391
36	4033
37	137438953471
38	174763
39	9588151
40	61681

[1, 3, 7, 5, 31, 1, 127, 17, 73, 11, 2047, 13, 8191, 43, 151, 257, 131071, 19, 524287, 41, 337, 683, 8388607, 241, 1082401, 2731, 262657, 3277, 536870911, 331, 2147483647, 65537, 599479, 43691, 8727391, 4033, 137438953471, 174763, 9588151, 61681]

cp's OEIS Frontend

A064078 Zsigmondy numbers for a = 2, b = 1: Zs(n, 2, 1) is the greatest divisor of 2^n - 1 (A000225) that is coprime to 2^m - 1 for all positive integers m < n.

Table of values

List of values