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 | 3 |
| 3 | 17 |
| 4 | 74 |
| 5 | 514 |
| 6 | 3564 |
| 7 | 30708 |
| 8 | 250704 |
| 9 | 2780496 |
| 10 | 29982240 |
| 11 | 373350240 |
| 12 | 4639870080 |
| 13 | 67024333440 |
| 14 | 988156834560 |
| 15 | 16914631507200 |
| 16 | 271941778483200 |
| 17 | 4999620452198400 |
| 18 | 94617104704819200 |
| 19 | 1925772463506124800 |
| 20 | 39245319872575488000 |
| 21 | 902004581585737728000 |