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This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A320855 Number of 9-element subsets of [n] whose sum is a triangular number.

Table of values

n a(n)
9 1
10 1
11 6
12 21
13 64
14 174
15 419
16 930
17 1921
18 3741
19 6933
20 12303
21 21044
22 34839
23 56044
24 87885
25 134682
26 202181
27 297873
28 431423
29 615166
30 864673
31 1199421
32 1643537
33 2226716
34 2985188
35 3962845
36 5212562
37 6797615
38 8793297
39 11288719
40 14388852
41 18216738
42 22915930
43 28653268

List of values

[1, 1, 6, 21, 64, 174, 419, 930, 1921, 3741, 6933, 12303, 21044, 34839, 56044, 87885, 134682, 202181, 297873, 431423, 615166, 864673, 1199421, 1643537, 2226716, 2985188, 3962845, 5212562, 6797615, 8793297, 11288719, 14388852, 18216738, 22915930, 28653268]

Started in 1964 by Neil J. A. Sloane | Maintained by The OEIS Foundation Inc.

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