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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 14 |
| 5 | 64 |
| 6 | 426 |
| 7 | 2790 |
| 8 | 24024 |
| 9 | 205056 |
| 10 | 2170680 |
| 11 | 22852200 |
| 12 | 287250480 |
| 13 | 3597143040 |
| 14 | 52370755920 |
| 15 | 760381337520 |
| 16 | 12585067447680 |
| 17 | 207863095910400 |
| 18 | 3854801333416320 |
| 19 | 71370457471716480 |
| 20 | 1465957162768492800 |
| 21 | 30071395843421184000 |
| 22 | 677696237345719468800 |