A344373 - cp's OEIS frontend

A344373 a(n) = Sum_{k=1..n-1} (-1)^k gcd(k, n).

n	a(n)
1	0
2	-1
3	0
4	0
5	0
6	-1
7	0
8	4
9	0
10	-1
11	0
12	8
13	0
14	-1
15	0
16	16
17	0
18	3
19	0
20	16
21	0
22	-1
23	0
24	36
25	0
26	-1
27	0
28	24
29	0
30	15
31	0
32	48
33	0
34	-1
35	0
36	48
37	0
38	-1
39	0
40	68
41	0
42	23
43	0
44	40
45	0
46	-1
47	0
48	112
49	0
50	15
51	0
52	48
53	0
54	27
55	0
56	100
57	0
58	-1
59	0
60	120
61	0
62	-1
63	0
64	128
65	0
66	39
67	0
68	64
69	0
70	47
71	0
72	180
73	0
74	-1
75	0
76	72
77	0
78	47
79	0
80	208
81	0
82	-1
83	0
84	176
85	0
86	-1
87	0
88	164
89	0
90	99

[0, -1, 0, 0, 0, -1, 0, 4, 0, -1, 0, 8, 0, -1, 0, 16, 0, 3, 0, 16, 0, -1, 0, 36, 0, -1, 0, 24, 0, 15, 0, 48, 0, -1, 0, 48, 0, -1, 0, 68, 0, 23, 0, 40, 0, -1, 0, 112, 0, 15, 0, 48, 0, 27, 0, 100, 0, -1, 0, 120, 0, -1, 0, 128, 0, 39, 0, 64, 0, 47, 0, 180, 0, -1, 0, 72, 0, 47, 0, 208, 0, -1, 0, 176, 0, -1, 0, 164, 0, 99]

cp's OEIS Frontend

A344373 a(n) = Sum_{k=1..n-1} (-1)^k gcd(k, n).

Table of values

List of values

n	a(n)
1	0
2	-1
3	0
4	0
5	0
6	-1
7	0
8	4
9	0
10	-1
11	0
12	8
13	0
14	-1
15	0
16	16
17	0
18	3
19	0
20	16
21	0
22	-1
23	0
24	36
25	0
26	-1
27	0
28	24
29	0
30	15
31	0
32	48
33	0
34	-1
35	0
36	48
37	0
38	-1
39	0
40	68
41	0
42	23
43	0
44	40
45	0
46	-1
47	0
48	112
49	0
50	15
51	0
52	48
53	0
54	27
55	0
56	100
57	0
58	-1
59	0
60	120
61	0
62	-1
63	0
64	128
65	0
66	39
67	0
68	64
69	0
70	47
71	0
72	180
73	0
74	-1
75	0
76	72
77	0
78	47
79	0
80	208
81	0
82	-1
83	0
84	176
85	0
86	-1
87	0
88	164
89	0
90	99

n	a(n)
1	0
2	-1
3	0
4	0
5	0
6	-1
7	0
8	4
9	0
10	-1
11	0
12	8
13	0
14	-1
15	0
16	16
17	0
18	3
19	0
20	16
21	0
22	-1
23	0
24	36
25	0
26	-1
27	0
28	24
29	0
30	15
31	0
32	48
33	0
34	-1
35	0
36	48
37	0
38	-1
39	0
40	68
41	0
42	23
43	0
44	40
45	0
46	-1
47	0
48	112
49	0
50	15
51	0
52	48
53	0
54	27
55	0
56	100
57	0
58	-1
59	0
60	120
61	0
62	-1
63	0
64	128
65	0
66	39
67	0
68	64
69	0
70	47
71	0
72	180
73	0
74	-1
75	0
76	72
77	0
78	47
79	0
80	208
81	0
82	-1
83	0
84	176
85	0
86	-1
87	0
88	164
89	0
90	99

n	a(n)
1	0
2	-1
3	0
4	0
5	0
6	-1
7	0
8	4
9	0
10	-1
11	0
12	8
13	0
14	-1
15	0
16	16
17	0
18	3
19	0
20	16
21	0
22	-1
23	0
24	36
25	0
26	-1
27	0
28	24
29	0
30	15
31	0
32	48
33	0
34	-1
35	0
36	48
37	0
38	-1
39	0
40	68
41	0
42	23
43	0
44	40
45	0
46	-1
47	0
48	112
49	0
50	15
51	0
52	48
53	0
54	27
55	0
56	100
57	0
58	-1
59	0
60	120
61	0
62	-1
63	0
64	128
65	0
66	39
67	0
68	64
69	0
70	47
71	0
72	180
73	0
74	-1
75	0
76	72
77	0
78	47
79	0
80	208
81	0
82	-1
83	0
84	176
85	0
86	-1
87	0
88	164
89	0
90	99