A259542 - cp's OEIS frontend

A259542 a(1) = 1, for n > 1 a(n) = smallest number not already in the sequence such that the arithmetic mean of two neighboring terms is a triangular number.

n	a(n)
1	1
2	5
3	7
4	13
5	17
6	3
7	9
8	11
9	19
10	23
11	33
12	39
13	51
14	21
15	35
16	37
17	53
18	57
19	15
20	27
21	29
22	43
23	47
24	25
25	31
26	41
27	49
28	61
29	71
30	85
31	97
32	59
33	73
34	83
35	99
36	111
37	45
38	65
39	67
40	89
41	93
42	63
43	69
44	87
45	95
46	115
47	125
48	147
49	159
50	81
51	75
52	107
53	103
54	79
55	77
56	55
57	101
58	109
59	131
60	141
61	165
62	177

[1, 5, 7, 13, 17, 3, 9, 11, 19, 23, 33, 39, 51, 21, 35, 37, 53, 57, 15, 27, 29, 43, 47, 25, 31, 41, 49, 61, 71, 85, 97, 59, 73, 83, 99, 111, 45, 65, 67, 89, 93, 63, 69, 87, 95, 115, 125, 147, 159, 81, 75, 107, 103, 79, 77, 55, 101, 109, 131, 141, 165, 177]

cp's OEIS Frontend

A259542 a(1) = 1, for n > 1 a(n) = smallest number not already in the sequence such that the arithmetic mean of two neighboring terms is a triangular number.

Table of values

List of values

n	a(n)
1	1
2	5
3	7
4	13
5	17
6	3
7	9
8	11
9	19
10	23
11	33
12	39
13	51
14	21
15	35
16	37
17	53
18	57
19	15
20	27
21	29
22	43
23	47
24	25
25	31
26	41
27	49
28	61
29	71
30	85
31	97
32	59
33	73
34	83
35	99
36	111
37	45
38	65
39	67
40	89
41	93
42	63
43	69
44	87
45	95
46	115
47	125
48	147
49	159
50	81
51	75
52	107
53	103
54	79
55	77
56	55
57	101
58	109
59	131
60	141
61	165
62	177

n	a(n)
1	1
2	5
3	7
4	13
5	17
6	3
7	9
8	11
9	19
10	23
11	33
12	39
13	51
14	21
15	35
16	37
17	53
18	57
19	15
20	27
21	29
22	43
23	47
24	25
25	31
26	41
27	49
28	61
29	71
30	85
31	97
32	59
33	73
34	83
35	99
36	111
37	45
38	65
39	67
40	89
41	93
42	63
43	69
44	87
45	95
46	115
47	125
48	147
49	159
50	81
51	75
52	107
53	103
54	79
55	77
56	55
57	101
58	109
59	131
60	141
61	165
62	177

n	a(n)
1	1
2	5
3	7
4	13
5	17
6	3
7	9
8	11
9	19
10	23
11	33
12	39
13	51
14	21
15	35
16	37
17	53
18	57
19	15
20	27
21	29
22	43
23	47
24	25
25	31
26	41
27	49
28	61
29	71
30	85
31	97
32	59
33	73
34	83
35	99
36	111
37	45
38	65
39	67
40	89
41	93
42	63
43	69
44	87
45	95
46	115
47	125
48	147
49	159
50	81
51	75
52	107
53	103
54	79
55	77
56	55
57	101
58	109
59	131
60	141
61	165
62	177