A111138 - cp's OEIS frontend

A111138 Let b(n) denote the number of nontriangular numbers less than or equal to n. Then a(n) = b(n-1) + a(b(n-1)), with a(1) = a(2) = 0, a(3) = 1.

n	a(n)
1	0
2	0
3	1
4	1
5	2
6	4
7	4
8	5
9	7
10	10
11	10
12	11
13	13
14	16
15	20
16	20
17	21
18	23
19	26
20	30
21	35
22	35
23	36
24	38
25	41
26	45
27	50
28	56
29	56
30	57
31	59
32	62
33	66
34	71
35	77
36	84
37	84
38	85
39	87
40	90
41	94
42	99
43	105
44	112
45	120
46	120
47	121
48	123
49	126
50	130
51	135
52	141
53	148
54	156
55	165
56	165
57	166
58	168
59	171
60	175
61	180
62	186
63	193
64	201

[0, 0, 1, 1, 2, 4, 4, 5, 7, 10, 10, 11, 13, 16, 20, 20, 21, 23, 26, 30, 35, 35, 36, 38, 41, 45, 50, 56, 56, 57, 59, 62, 66, 71, 77, 84, 84, 85, 87, 90, 94, 99, 105, 112, 120, 120, 121, 123, 126, 130, 135, 141, 148, 156, 165, 165, 166, 168, 171, 175, 180, 186, 193, 201]

cp's OEIS Frontend

A111138 Let b(n) denote the number of nontriangular numbers less than or equal to n. Then a(n) = b(n-1) + a(b(n-1)), with a(1) = a(2) = 0, a(3) = 1.

Table of values

List of values

n	a(n)
1	0
2	0
3	1
4	1
5	2
6	4
7	4
8	5
9	7
10	10
11	10
12	11
13	13
14	16
15	20
16	20
17	21
18	23
19	26
20	30
21	35
22	35
23	36
24	38
25	41
26	45
27	50
28	56
29	56
30	57
31	59
32	62
33	66
34	71
35	77
36	84
37	84
38	85
39	87
40	90
41	94
42	99
43	105
44	112
45	120
46	120
47	121
48	123
49	126
50	130
51	135
52	141
53	148
54	156
55	165
56	165
57	166
58	168
59	171
60	175
61	180
62	186
63	193
64	201

n	a(n)
1	0
2	0
3	1
4	1
5	2
6	4
7	4
8	5
9	7
10	10
11	10
12	11
13	13
14	16
15	20
16	20
17	21
18	23
19	26
20	30
21	35
22	35
23	36
24	38
25	41
26	45
27	50
28	56
29	56
30	57
31	59
32	62
33	66
34	71
35	77
36	84
37	84
38	85
39	87
40	90
41	94
42	99
43	105
44	112
45	120
46	120
47	121
48	123
49	126
50	130
51	135
52	141
53	148
54	156
55	165
56	165
57	166
58	168
59	171
60	175
61	180
62	186
63	193
64	201

n	a(n)
1	0
2	0
3	1
4	1
5	2
6	4
7	4
8	5
9	7
10	10
11	10
12	11
13	13
14	16
15	20
16	20
17	21
18	23
19	26
20	30
21	35
22	35
23	36
24	38
25	41
26	45
27	50
28	56
29	56
30	57
31	59
32	62
33	66
34	71
35	77
36	84
37	84
38	85
39	87
40	90
41	94
42	99
43	105
44	112
45	120
46	120
47	121
48	123
49	126
50	130
51	135
52	141
53	148
54	156
55	165
56	165
57	166
58	168
59	171
60	175
61	180
62	186
63	193
64	201