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) |
|---|---|
| 3 | 1 |
| 4 | 0 |
| 5 | 10 |
| 6 | 20 |
| 7 | 140 |
| 8 | 616 |
| 9 | 3444 |
| 10 | 19440 |
| 11 | 117975 |
| 12 | 753500 |
| 13 | 5068492 |
| 14 | 35764092 |
| 15 | 264044235 |
| 16 | 2034636800 |
| 17 | 16327586760 |
| 18 | 136180742640 |
| 19 | 1178372198220 |
| 20 | 10561041814380 |
| 21 | 97889061389210 |
| 22 | 937053052507880 |
| 23 | 9252175434771885 |
| 24 | 94115781485796488 |
| 25 | 985250825472122200 |