A075019 - cp's OEIS frontend

A075019 a(1) = 1; for n > 1, a(n) = the smallest prime divisor of the number C(n) formed from the concatenation of 1,2,3,... up to n.

n	a(n)
1	1
2	2
3	3
4	2
5	3
6	2
7	127
8	2
9	3
10	2
11	3
12	2
13	113
14	2
15	3
16	2
17	3
18	2
19	13
20	2
21	3
22	2
23	3
24	2
25	5
26	2
27	3
28	2
29	3
30	2
31	29
32	2
33	3
34	2
35	3
36	2
37	71
38	2
39	3
40	2
41	3
42	2
43	7
44	2
45	3
46	2
47	3
48	2
49	23
50	2
51	3
52	2
53	3
54	2
55	5
56	2
57	3
58	2
59	3
60	2
61	10386763
62	2
63	3
64	2
65	3
66	2
67	397
68	2
69	3
70	2
71	3
72	2
73	37907
74	2
75	3
76	2
77	3
78	2
79	73
80	2
81	3
82	2
83	3
84	2
85	5
86	2
87	3
88	2
89	3
90	2
91	37
92	2
93	3
94	2

[1, 2, 3, 2, 3, 2, 127, 2, 3, 2, 3, 2, 113, 2, 3, 2, 3, 2, 13, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 29, 2, 3, 2, 3, 2, 71, 2, 3, 2, 3, 2, 7, 2, 3, 2, 3, 2, 23, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 10386763, 2, 3, 2, 3, 2, 397, 2, 3, 2, 3, 2, 37907, 2, 3, 2, 3, 2, 73, 2, 3, 2, 3, 2, 5, 2, 3, 2, 3, 2, 37, 2, 3, 2]

cp's OEIS Frontend

A075019 a(1) = 1; for n > 1, a(n) = the smallest prime divisor of the number C(n) formed from the concatenation of 1,2,3,... up to n.

Table of values

List of values