A379775 - cp's OEIS frontend

A379775 a(1) = 2. For n > 1, a(n) = smallest prime factor of c=2a(n-1)-1 that is not in {a(1), ..., a(n-1)}; if all prime factors of c are in {a(1), ..., a(n-1)}, then we try the next value of c, which is 2c-1; and so on.

n	a(n)
1	2
2	3
3	5
4	17
5	11
6	7
7	13
8	97
9	193
10	769
11	29
12	19
13	37
14	73
15	577
16	1153
17	461
18	307
19	613
20	31
21	61
22	241
23	113
24	449
25	23
26	89
27	59
28	233
29	929
30	619
31	1237
32	2473
33	43
34	337
35	673
36	269
37	179
38	211
39	421
40	41
41	107
42	71
43	47
44	67
45	53
46	139
47	277
48	79
49	157
50	313
51	1249
52	227
53	151
54	601
55	1201
56	4801

[2, 3, 5, 17, 11, 7, 13, 97, 193, 769, 29, 19, 37, 73, 577, 1153, 461, 307, 613, 31, 61, 241, 113, 449, 23, 89, 59, 233, 929, 619, 1237, 2473, 43, 337, 673, 269, 179, 211, 421, 41, 107, 71, 47, 67, 53, 139, 277, 79, 157, 313, 1249, 227, 151, 601, 1201, 4801]

cp's OEIS Frontend

A379775 a(1) = 2. For n > 1, a(n) = smallest prime factor of c=2a(n-1)-1 that is not in {a(1), ..., a(n-1)}; if all prime factors of c are in {a(1), ..., a(n-1)}, then we try the next value of c, which is 2c-1; and so on.

Table of values

List of values

cp's OEIS Frontend

A379775 a(1) = 2. For n > 1, a(n) = smallest prime factor of c=2*a(n-1)-1 that is not in {a(1), ..., a(n-1)}; if all prime factors of c are in {a(1), ..., a(n-1)}, then we try the next value of c, which is 2*c-1; and so on.

Table of values

List of values

A379775 a(1) = 2. For n > 1, a(n) = smallest prime factor of c=2a(n-1)-1 that is not in {a(1), ..., a(n-1)}; if all prime factors of c are in {a(1), ..., a(n-1)}, then we try the next value of c, which is 2c-1; and so on.