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 | 2 |
| 3 | 12 |
| 4 | 72 |
| 5 | 540 |
| 6 | 4668 |
| 7 | 47292 |
| 8 | 545760 |
| 9 | 7087248 |
| 10 | 102247020 |
| 11 | 1622632572 |
| 12 | 28091562840 |
| 13 | 526858348380 |
| 14 | 10641342923148 |
| 15 | 230283190977300 |
| 16 | 5315654681435520 |
| 17 | 130370767029135900 |
| 18 | 3385534663249753392 |
| 19 | 92801587319328411132 |
| 20 | 2677687796244281955480 |
| 21 | 81124824998504073834516 |