A025731 - OEIS

A025731 as a simple table

n	a(n)
1	1
2	3
3	6
4	10
5	15
6	21
7	28
8	36
9	45
10	55
11	66
12	78
13	91
14	105
15	120
16	137
17	155
18	174
19	194
20	215
21	237
22	260
23	284
24	309
25	335
26	362
27	390
28	419
29	449
30	480
31	513
32	547
33	582
34	618
35	655
36	693
37	732
38	772
39	813
40	855
41	898
42	942
43	987
44	1033
45	1081
46	1130
47	1180
48	1231
49	1283
50	1336
51	1390
52	1445
53	1501
54	1558
55	1616

[1,3,6,10,15,21,28,36,45,55,66,78,91,105,120,137, 155,174,194,215,237,260,284,309,335,362,390,419, 449,480,513,547,582,618,655,693,732,772,813,855, 898,942,987,1033,1081,1130,1180,1231,1283,1336, 1390,1445,1501,1558,1616]