A077220 - cp's OEIS frontend

A077220 a(1) = 1; thereafter a(n) is smallest number not occurring earlier such that a(n-1)+a(n) is a triangular number.

n	a(n)
1	1
2	2
3	4
4	6
5	9
6	12
7	3
8	7
9	8
10	13
11	15
12	21
13	24
14	31
15	5
16	10
17	11
18	17
19	19
20	26
21	29
22	16
23	20
24	25
25	30
26	36
27	42
28	49
29	56
30	22
31	14
32	41
33	37
34	18
35	27
36	28
37	38
38	40
39	51
40	54
41	66
42	39
43	52
44	53
45	67
46	69
47	84
48	87
49	33
50	45
51	46
52	32
53	23
54	43
55	35
56	70
57	50
58	55
59	65
60	71
61	34
62	44
63	47
64	58
65	62
66	74
67	79
68	57
69	48
70	72
71	64
72	89

[1, 2, 4, 6, 9, 12, 3, 7, 8, 13, 15, 21, 24, 31, 5, 10, 11, 17, 19, 26, 29, 16, 20, 25, 30, 36, 42, 49, 56, 22, 14, 41, 37, 18, 27, 28, 38, 40, 51, 54, 66, 39, 52, 53, 67, 69, 84, 87, 33, 45, 46, 32, 23, 43, 35, 70, 50, 55, 65, 71, 34, 44, 47, 58, 62, 74, 79, 57, 48, 72, 64, 89]

cp's OEIS Frontend

A077220 a(1) = 1; thereafter a(n) is smallest number not occurring earlier such that a(n-1)+a(n) is a triangular number.

Table of values

List of values

n	a(n)
1	1
2	2
3	4
4	6
5	9
6	12
7	3
8	7
9	8
10	13
11	15
12	21
13	24
14	31
15	5
16	10
17	11
18	17
19	19
20	26
21	29
22	16
23	20
24	25
25	30
26	36
27	42
28	49
29	56
30	22
31	14
32	41
33	37
34	18
35	27
36	28
37	38
38	40
39	51
40	54
41	66
42	39
43	52
44	53
45	67
46	69
47	84
48	87
49	33
50	45
51	46
52	32
53	23
54	43
55	35
56	70
57	50
58	55
59	65
60	71
61	34
62	44
63	47
64	58
65	62
66	74
67	79
68	57
69	48
70	72
71	64
72	89

n	a(n)
1	1
2	2
3	4
4	6
5	9
6	12
7	3
8	7
9	8
10	13
11	15
12	21
13	24
14	31
15	5
16	10
17	11
18	17
19	19
20	26
21	29
22	16
23	20
24	25
25	30
26	36
27	42
28	49
29	56
30	22
31	14
32	41
33	37
34	18
35	27
36	28
37	38
38	40
39	51
40	54
41	66
42	39
43	52
44	53
45	67
46	69
47	84
48	87
49	33
50	45
51	46
52	32
53	23
54	43
55	35
56	70
57	50
58	55
59	65
60	71
61	34
62	44
63	47
64	58
65	62
66	74
67	79
68	57
69	48
70	72
71	64
72	89

n	a(n)
1	1
2	2
3	4
4	6
5	9
6	12
7	3
8	7
9	8
10	13
11	15
12	21
13	24
14	31
15	5
16	10
17	11
18	17
19	19
20	26
21	29
22	16
23	20
24	25
25	30
26	36
27	42
28	49
29	56
30	22
31	14
32	41
33	37
34	18
35	27
36	28
37	38
38	40
39	51
40	54
41	66
42	39
43	52
44	53
45	67
46	69
47	84
48	87
49	33
50	45
51	46
52	32
53	23
54	43
55	35
56	70
57	50
58	55
59	65
60	71
61	34
62	44
63	47
64	58
65	62
66	74
67	79
68	57
69	48
70	72
71	64
72	89