A171772 - cp's OEIS frontend

A171772 Number of steps needed to reach a prime when the map S(n)+M(n) is applied to n, or -1 if a prime is never reached. Here S(n) and M(N) mean the sum and the product of the digits of n in base 10.

n	a(n)
1	1
2	0
3	0
4	3
5	0
6	2
7	0
8	2
9	2
10	2
11	0
12	1
13	0
14	3
15	1
16	1
17	0
18	1
19	0
20	1
21	1
22	3
23	0
24	4
25	1
26	2
27	1
28	3
29	0
30	1
31	0
32	1
33	2
34	1
35	1
36	2
37	0
38	2
39	-1
40	4
41	0
42	4
43	0
44	5
45	1
46	2
47	0
48	6
49	-1
50	1
51	1
52	1
53	0
54	1
55	2
56	1
57	1
58	1
59	0
60	3
61	0
62	2
63	2
64	2
65	1
66	7
67	0
68	3
69	-1
70	1
71	0
72	1
73	0
74	-1
75	1
76	3
77	3
78	1
79	0
80	3

[1, 0, 0, 3, 0, 2, 0, 2, 2, 2, 0, 1, 0, 3, 1, 1, 0, 1, 0, 1, 1, 3, 0, 4, 1, 2, 1, 3, 0, 1, 0, 1, 2, 1, 1, 2, 0, 2, -1, 4, 0, 4, 0, 5, 1, 2, 0, 6, -1, 1, 1, 1, 0, 1, 2, 1, 1, 1, 0, 3, 0, 2, 2, 2, 1, 7, 0, 3, -1, 1, 0, 1, 0, -1, 1, 3, 3, 1, 0, 3]

cp's OEIS Frontend

A171772 Number of steps needed to reach a prime when the map S(n)+M(n) is applied to n, or -1 if a prime is never reached. Here S(n) and M(N) mean the sum and the product of the digits of n in base 10.

Table of values

List of values

n	a(n)
1	1
2	0
3	0
4	3
5	0
6	2
7	0
8	2
9	2
10	2
11	0
12	1
13	0
14	3
15	1
16	1
17	0
18	1
19	0
20	1
21	1
22	3
23	0
24	4
25	1
26	2
27	1
28	3
29	0
30	1
31	0
32	1
33	2
34	1
35	1
36	2
37	0
38	2
39	-1
40	4
41	0
42	4
43	0
44	5
45	1
46	2
47	0
48	6
49	-1
50	1
51	1
52	1
53	0
54	1
55	2
56	1
57	1
58	1
59	0
60	3
61	0
62	2
63	2
64	2
65	1
66	7
67	0
68	3
69	-1
70	1
71	0
72	1
73	0
74	-1
75	1
76	3
77	3
78	1
79	0
80	3

n	a(n)
1	1
2	0
3	0
4	3
5	0
6	2
7	0
8	2
9	2
10	2
11	0
12	1
13	0
14	3
15	1
16	1
17	0
18	1
19	0
20	1
21	1
22	3
23	0
24	4
25	1
26	2
27	1
28	3
29	0
30	1
31	0
32	1
33	2
34	1
35	1
36	2
37	0
38	2
39	-1
40	4
41	0
42	4
43	0
44	5
45	1
46	2
47	0
48	6
49	-1
50	1
51	1
52	1
53	0
54	1
55	2
56	1
57	1
58	1
59	0
60	3
61	0
62	2
63	2
64	2
65	1
66	7
67	0
68	3
69	-1
70	1
71	0
72	1
73	0
74	-1
75	1
76	3
77	3
78	1
79	0
80	3

n	a(n)
1	1
2	0
3	0
4	3
5	0
6	2
7	0
8	2
9	2
10	2
11	0
12	1
13	0
14	3
15	1
16	1
17	0
18	1
19	0
20	1
21	1
22	3
23	0
24	4
25	1
26	2
27	1
28	3
29	0
30	1
31	0
32	1
33	2
34	1
35	1
36	2
37	0
38	2
39	-1
40	4
41	0
42	4
43	0
44	5
45	1
46	2
47	0
48	6
49	-1
50	1
51	1
52	1
53	0
54	1
55	2
56	1
57	1
58	1
59	0
60	3
61	0
62	2
63	2
64	2
65	1
66	7
67	0
68	3
69	-1
70	1
71	0
72	1
73	0
74	-1
75	1
76	3
77	3
78	1
79	0
80	3