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 | 1 |
| 2 | 5 |
| 3 | 24 |
| 4 | 132 |
| 5 | 840 |
| 6 | 6120 |
| 7 | 50400 |
| 8 | 463680 |
| 9 | 4717440 |
| 10 | 52617600 |
| 11 | 638668800 |
| 12 | 8382528000 |
| 13 | 118313395200 |
| 14 | 1787154969600 |
| 15 | 28768836096000 |
| 16 | 491685562368000 |
| 17 | 8892185702400000 |
| 18 | 169662903201792000 |
| 19 | 3406062811447296000 |
| 20 | 71770609241210880000 |
| 21 | 1583819207322992640000 |