A292771 - cp's OEIS frontend

A292771 If sigma(n)-phi(n) is even then (sigma(n)-phi(n))/2 otherwise -1.

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

[0, 1, 1, -1, 1, 5, 1, -1, -1, 7, 1, 12, 1, 9, 8, -1, 1, -1, 1, 17, 10, 13, 1, 26, -1, 15, 11, 22, 1, 32, 1, -1, 14, 19, 12, -1, 1, 21, 16, 37, 1, 42, 1, 32, 27, 25, 1, 54, -1, -1, 20, 37, 1, 51, 16, 48, 22, 31, 1, 76, 1, 33, 34, -1, 18, 62, 1, 47, 26, 60, 1, -1, 1, 39, 42, 52, 18, 72, 1, 77, -1, 43, 1]

cp's OEIS Frontend

A292771 If sigma(n)-phi(n) is even then (sigma(n)-phi(n))/2 otherwise -1.

Table of values

List of values

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

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

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