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 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 12 |
| 4 | 74 |
| 5 | 540 |
| 6 | 4682 |
| 7 | 47292 |
| 8 | 545834 |
| 9 | 7087260 |
| 10 | 102247562 |
| 11 | 1622632572 |
| 12 | 28091567594 |
| 13 | 526858348380 |
| 14 | 10641342970442 |
| 15 | 230283190977852 |
| 16 | 5315654681981354 |
| 17 | 130370767029135900 |
| 18 | 3385534663256845322 |
| 19 | 92801587319328411132 |
| 20 | 2677687796244384203114 |
| 21 | 81124824998504073881820 |