A292770 - cp's OEIS frontend

A292770 If sigma(n)+phi(n) is even then a(n) = (sigma(n)+phi(n))/2 otherwise -1.

n	a(n)
1	1
2	2
3	3
4	-1
5	5
6	7
7	7
8	-1
9	-1
10	11
11	11
12	16
13	13
14	15
15	16
16	-1
17	17
18	-1
19	19
20	25
21	22
22	23
23	23
24	34
25	-1
26	27
27	29
28	34
29	29
30	40
31	31
32	-1
33	34
34	35
35	36
36	-1
37	37
38	39
39	40
40	53
41	41
42	54
43	43
44	52
45	51
46	47
47	47
48	70
49	-1
50	-1
51	52
52	61
53	53
54	69
55	56
56	72
57	58
58	59
59	59
60	92
61	61
62	63
63	70
64	-1
65	66
66	82
67	67
68	79
69	70
70	84
71	71
72	-1
73	73
74	75
75	82
76	88
77	78
78	96

[1, 2, 3, -1, 5, 7, 7, -1, -1, 11, 11, 16, 13, 15, 16, -1, 17, -1, 19, 25, 22, 23, 23, 34, -1, 27, 29, 34, 29, 40, 31, -1, 34, 35, 36, -1, 37, 39, 40, 53, 41, 54, 43, 52, 51, 47, 47, 70, -1, -1, 52, 61, 53, 69, 56, 72, 58, 59, 59, 92, 61, 63, 70, -1, 66, 82, 67, 79, 70, 84, 71, -1, 73, 75, 82, 88, 78, 96]

cp's OEIS Frontend

A292770 If sigma(n)+phi(n) is even then a(n) = (sigma(n)+phi(n))/2 otherwise -1.

Table of values

List of values

n	a(n)
1	1
2	2
3	3
4	-1
5	5
6	7
7	7
8	-1
9	-1
10	11
11	11
12	16
13	13
14	15
15	16
16	-1
17	17
18	-1
19	19
20	25
21	22
22	23
23	23
24	34
25	-1
26	27
27	29
28	34
29	29
30	40
31	31
32	-1
33	34
34	35
35	36
36	-1
37	37
38	39
39	40
40	53
41	41
42	54
43	43
44	52
45	51
46	47
47	47
48	70
49	-1
50	-1
51	52
52	61
53	53
54	69
55	56
56	72
57	58
58	59
59	59
60	92
61	61
62	63
63	70
64	-1
65	66
66	82
67	67
68	79
69	70
70	84
71	71
72	-1
73	73
74	75
75	82
76	88
77	78
78	96

n	a(n)
1	1
2	2
3	3
4	-1
5	5
6	7
7	7
8	-1
9	-1
10	11
11	11
12	16
13	13
14	15
15	16
16	-1
17	17
18	-1
19	19
20	25
21	22
22	23
23	23
24	34
25	-1
26	27
27	29
28	34
29	29
30	40
31	31
32	-1
33	34
34	35
35	36
36	-1
37	37
38	39
39	40
40	53
41	41
42	54
43	43
44	52
45	51
46	47
47	47
48	70
49	-1
50	-1
51	52
52	61
53	53
54	69
55	56
56	72
57	58
58	59
59	59
60	92
61	61
62	63
63	70
64	-1
65	66
66	82
67	67
68	79
69	70
70	84
71	71
72	-1
73	73
74	75
75	82
76	88
77	78
78	96

n	a(n)
1	1
2	2
3	3
4	-1
5	5
6	7
7	7
8	-1
9	-1
10	11
11	11
12	16
13	13
14	15
15	16
16	-1
17	17
18	-1
19	19
20	25
21	22
22	23
23	23
24	34
25	-1
26	27
27	29
28	34
29	29
30	40
31	31
32	-1
33	34
34	35
35	36
36	-1
37	37
38	39
39	40
40	53
41	41
42	54
43	43
44	52
45	51
46	47
47	47
48	70
49	-1
50	-1
51	52
52	61
53	53
54	69
55	56
56	72
57	58
58	59
59	59
60	92
61	61
62	63
63	70
64	-1
65	66
66	82
67	67
68	79
69	70
70	84
71	71
72	-1
73	73
74	75
75	82
76	88
77	78
78	96