A213980 - cp's OEIS frontend

A213980 Let n = prime(1)^c_1 * prime(2)^c_2 * ... * prime(k)^c_k be the prime factorization of n. Set f(n) = n - 1 + c_1 + c_2 + ... + c_k and f_i, i>=0 (f_0(n) = n, f_1=f) is i-th iteration of f. a(n) is the minimal i such that f_i(n) is prime.

n	a(n)
2	0
3	0
4	1
5	0
6	1
7	0
8	2
9	2
10	1
11	0
12	4
13	0
14	3
15	2
16	1
17	0
18	3
19	0
20	2
21	2
22	1
23	0
24	2
25	3
26	2
27	1
28	6
29	0
30	5
31	0
32	4
33	6
34	5
35	4
36	3
37	0
38	3
39	2
40	1
41	0
42	3
43	0
44	2
45	1
46	1
47	0
48	5
49	6
50	5
51	5
52	4
53	0
54	3
55	2
56	1
57	2
58	1
59	0
60	18
61	0
62	18
63	17
64	15
65	16
66	15
67	0
68	14
69	14
70	13
71	0
72	12
73	0
74	13
75	12
76	11
77	11
78	10
79	0
80	9
81	9
82	1
83	0
84	8
85	9
86	8
87	7
88	6
89	0
90	5
91	5
92	4
93	4
94	3
95	2
96	1
97	0
98	2
99	1
100	1
101	0
102	2
103	0
104	1
105	1
106	1
107	0
108	16
109	0

[0, 0, 1, 0, 1, 0, 2, 2, 1, 0, 4, 0, 3, 2, 1, 0, 3, 0, 2, 2, 1, 0, 2, 3, 2, 1, 6, 0, 5, 0, 4, 6, 5, 4, 3, 0, 3, 2, 1, 0, 3, 0, 2, 1, 1, 0, 5, 6, 5, 5, 4, 0, 3, 2, 1, 2, 1, 0, 18, 0, 18, 17, 15, 16, 15, 0, 14, 14, 13, 0, 12, 0, 13, 12, 11, 11, 10, 0, 9, 9, 1, 0, 8, 9, 8, 7, 6, 0, 5, 5, 4, 4, 3, 2, 1, 0, 2, 1, 1, 0, 2, 0, 1, 1, 1, 0, 16, 0]

cp's OEIS Frontend

A213980 Let n = prime(1)^c_1 * prime(2)^c_2 * ... * prime(k)^c_k be the prime factorization of n. Set f(n) = n - 1 + c_1 + c_2 + ... + c_k and f_i, i>=0 (f_0(n) = n, f_1=f) is i-th iteration of f. a(n) is the minimal i such that f_i(n) is prime.

Table of values

List of values

n	a(n)
2	0
3	0
4	1
5	0
6	1
7	0
8	2
9	2
10	1
11	0
12	4
13	0
14	3
15	2
16	1
17	0
18	3
19	0
20	2
21	2
22	1
23	0
24	2
25	3
26	2
27	1
28	6
29	0
30	5
31	0
32	4
33	6
34	5
35	4
36	3
37	0
38	3
39	2
40	1
41	0
42	3
43	0
44	2
45	1
46	1
47	0
48	5
49	6
50	5
51	5
52	4
53	0
54	3
55	2
56	1
57	2
58	1
59	0
60	18
61	0
62	18
63	17
64	15
65	16
66	15
67	0
68	14
69	14
70	13
71	0
72	12
73	0
74	13
75	12
76	11
77	11
78	10
79	0
80	9
81	9
82	1
83	0
84	8
85	9
86	8
87	7
88	6
89	0
90	5
91	5
92	4
93	4
94	3
95	2
96	1
97	0
98	2
99	1
100	1
101	0
102	2
103	0
104	1
105	1
106	1
107	0
108	16
109	0

n	a(n)
2	0
3	0
4	1
5	0
6	1
7	0
8	2
9	2
10	1
11	0
12	4
13	0
14	3
15	2
16	1
17	0
18	3
19	0
20	2
21	2
22	1
23	0
24	2
25	3
26	2
27	1
28	6
29	0
30	5
31	0
32	4
33	6
34	5
35	4
36	3
37	0
38	3
39	2
40	1
41	0
42	3
43	0
44	2
45	1
46	1
47	0
48	5
49	6
50	5
51	5
52	4
53	0
54	3
55	2
56	1
57	2
58	1
59	0
60	18
61	0
62	18
63	17
64	15
65	16
66	15
67	0
68	14
69	14
70	13
71	0
72	12
73	0
74	13
75	12
76	11
77	11
78	10
79	0
80	9
81	9
82	1
83	0
84	8
85	9
86	8
87	7
88	6
89	0
90	5
91	5
92	4
93	4
94	3
95	2
96	1
97	0
98	2
99	1
100	1
101	0
102	2
103	0
104	1
105	1
106	1
107	0
108	16
109	0

n	a(n)
2	0
3	0
4	1
5	0
6	1
7	0
8	2
9	2
10	1
11	0
12	4
13	0
14	3
15	2
16	1
17	0
18	3
19	0
20	2
21	2
22	1
23	0
24	2
25	3
26	2
27	1
28	6
29	0
30	5
31	0
32	4
33	6
34	5
35	4
36	3
37	0
38	3
39	2
40	1
41	0
42	3
43	0
44	2
45	1
46	1
47	0
48	5
49	6
50	5
51	5
52	4
53	0
54	3
55	2
56	1
57	2
58	1
59	0
60	18
61	0
62	18
63	17
64	15
65	16
66	15
67	0
68	14
69	14
70	13
71	0
72	12
73	0
74	13
75	12
76	11
77	11
78	10
79	0
80	9
81	9
82	1
83	0
84	8
85	9
86	8
87	7
88	6
89	0
90	5
91	5
92	4
93	4
94	3
95	2
96	1
97	0
98	2
99	1
100	1
101	0
102	2
103	0
104	1
105	1
106	1
107	0
108	16
109	0