A306801 - cp's OEIS frontend

A306801 An irregular fractal sequence: underline a(n) iff [a(n-1) + a(n)] is divisible by 3; all underlined terms rebuild the starting sequence.

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

[1, 3, 2, 1, 4, 6, 3, 5, 8, 9, 7, 2, 1, 10, 12, 11, 4, 13, 15, 6, 3, 14, 17, 18, 16, 5, 20, 21, 19, 8, 23, 24, 9, 22, 25, 27, 26, 7, 2, 1, 28, 30, 29, 10, 31, 33, 12, 32, 35, 36, 34, 11, 4, 37, 39, 38, 13, 40, 42, 15, 6, 3, 41, 44, 45, 43, 14, 47, 48, 46, 17, 50, 51, 18, 49, 52, 54, 53, 16, 5, 56, 57, 55, 20, 59, 60, 21, 58, 61, 63]

cp's OEIS Frontend

A306801 An irregular fractal sequence: underline a(n) iff [a(n-1) + a(n)] is divisible by 3; all underlined terms rebuild the starting sequence.

Table of values

List of values

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

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

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