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.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 6 |
| 4 | 15 |
| 5 | 21 |
| 6 | 45 |
| 7 | 111 |
| 8 | 261 |
| 9 | 1605 |
| 10 | 1995 |
| 11 | 4935 |
| 12 | 8295 |
| 13 | 69825 |
| 14 | 268155 |
| 15 | 550725 |
| 16 | 4574955 |
| 17 | 12024855 |
| 18 | 39867135 |
| 19 | 398467245 |
| 20 | 1698754365 |
| 21 | 16351800465 |