A153023 - cp's OEIS frontend

A153023 If n is 1 or prime then a(n) = n. Otherwise, start with n and iterate the map k -> A048050(k) until we reach a prime p; then a(n) = p. If we never reach a prime, a(n) = -1. A048050 gives the sum of proper divisors of k, excluding both 1 and n from the sum.

n	a(n)
1	1
2	2
3	3
4	2
5	5
6	5
7	7
8	5
9	3
10	7
11	11
12	5
13	13
14	3
15	5
16	3
17	17
18	7
19	19
20	7
21	7
22	13
23	23
24	5
25	5
26	5
27	5
28	5
29	29
30	41
31	31
32	41
33	3
34	19
35	5
36	7
37	37
38	7
39	3
40	7
41	41
42	53
43	43
44	3
45	41
46	5
47	47
48	-1
49	7
50	53
51	7
52	41
53	53
54	7
55	3
56	7
57	13
58	31
59	59
60	107
61	61
62	3
63	7
64	3
65	7
66	7
67	67
68	13
69	5
70	73
71	71
72	7
73	73
74	3
75	-1
76	7
77	7
78	89
79	79
80	41
81	3
82	43
83	83
84	139
85	13

[1, 2, 3, 2, 5, 5, 7, 5, 3, 7, 11, 5, 13, 3, 5, 3, 17, 7, 19, 7, 7, 13, 23, 5, 5, 5, 5, 5, 29, 41, 31, 41, 3, 19, 5, 7, 37, 7, 3, 7, 41, 53, 43, 3, 41, 5, 47, -1, 7, 53, 7, 41, 53, 7, 3, 7, 13, 31, 59, 107, 61, 3, 7, 3, 7, 7, 67, 13, 5, 73, 71, 7, 73, 3, -1, 7, 7, 89, 79, 41, 3, 43, 83, 139, 13]

cp's OEIS Frontend

A153023 If n is 1 or prime then a(n) = n. Otherwise, start with n and iterate the map k -> A048050(k) until we reach a prime p; then a(n) = p. If we never reach a prime, a(n) = -1. A048050 gives the sum of proper divisors of k, excluding both 1 and n from the sum.

Table of values

List of values

n	a(n)
1	1
2	2
3	3
4	2
5	5
6	5
7	7
8	5
9	3
10	7
11	11
12	5
13	13
14	3
15	5
16	3
17	17
18	7
19	19
20	7
21	7
22	13
23	23
24	5
25	5
26	5
27	5
28	5
29	29
30	41
31	31
32	41
33	3
34	19
35	5
36	7
37	37
38	7
39	3
40	7
41	41
42	53
43	43
44	3
45	41
46	5
47	47
48	-1
49	7
50	53
51	7
52	41
53	53
54	7
55	3
56	7
57	13
58	31
59	59
60	107
61	61
62	3
63	7
64	3
65	7
66	7
67	67
68	13
69	5
70	73
71	71
72	7
73	73
74	3
75	-1
76	7
77	7
78	89
79	79
80	41
81	3
82	43
83	83
84	139
85	13

n	a(n)
1	1
2	2
3	3
4	2
5	5
6	5
7	7
8	5
9	3
10	7
11	11
12	5
13	13
14	3
15	5
16	3
17	17
18	7
19	19
20	7
21	7
22	13
23	23
24	5
25	5
26	5
27	5
28	5
29	29
30	41
31	31
32	41
33	3
34	19
35	5
36	7
37	37
38	7
39	3
40	7
41	41
42	53
43	43
44	3
45	41
46	5
47	47
48	-1
49	7
50	53
51	7
52	41
53	53
54	7
55	3
56	7
57	13
58	31
59	59
60	107
61	61
62	3
63	7
64	3
65	7
66	7
67	67
68	13
69	5
70	73
71	71
72	7
73	73
74	3
75	-1
76	7
77	7
78	89
79	79
80	41
81	3
82	43
83	83
84	139
85	13

n	a(n)
1	1
2	2
3	3
4	2
5	5
6	5
7	7
8	5
9	3
10	7
11	11
12	5
13	13
14	3
15	5
16	3
17	17
18	7
19	19
20	7
21	7
22	13
23	23
24	5
25	5
26	5
27	5
28	5
29	29
30	41
31	31
32	41
33	3
34	19
35	5
36	7
37	37
38	7
39	3
40	7
41	41
42	53
43	43
44	3
45	41
46	5
47	47
48	-1
49	7
50	53
51	7
52	41
53	53
54	7
55	3
56	7
57	13
58	31
59	59
60	107
61	61
62	3
63	7
64	3
65	7
66	7
67	67
68	13
69	5
70	73
71	71
72	7
73	73
74	3
75	-1
76	7
77	7
78	89
79	79
80	41
81	3
82	43
83	83
84	139
85	13