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 | 0 |
| 3 | 3 |
| 4 | 18 |
| 5 | 78 |
| 6 | 270 |
| 7 | 921 |
| 8 | 2898 |
| 9 | 9147 |
| 10 | 27987 |
| 11 | 85773 |
| 12 | 259557 |
| 13 | 785778 |
| 14 | 2366892 |
| 15 | 7128120 |
| 16 | 21425040 |
| 17 | 64382550 |
| 18 | 193316685 |
| 19 | 580372293 |
| 20 | 1741819245 |
| 21 | 5227115454 |
| 22 | 15684238080 |
| 23 | 47059266081 |
| 24 | 141189599250 |