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) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 20 |
| 3 | 220 |
| 4 | 2280 |
| 5 | 25920 |
| 6 | 443744 |
| 7 | 10057408 |
| 8 | 215047552 |
| 9 | 3841564160 |
| 10 | 57161584256 |
| 11 | 757459114112 |
| 12 | 10427052678656 |
| 13 | 166827795710208 |
| 14 | 2728593278189568 |
| 15 | 38108069305433088 |
| 16 | 521570277192555520 |
| 17 | 14195894062729323520 |
| 18 | 594582326909611536384 |
| 19 | 21399757674339677249536 |