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 | 0 |
| 2 | 1 |
| 3 | 7 |
| 4 | 46 |
| 5 | 326 |
| 6 | 2556 |
| 7 | 22212 |
| 8 | 212976 |
| 9 | 2239344 |
| 10 | 25659360 |
| 11 | 318540960 |
| 12 | 4261576320 |
| 13 | 61148511360 |
| 14 | 937030429440 |
| 15 | 15275952518400 |
| 16 | 264030355814400 |
| 17 | 4823280687052800 |
| 18 | 92865738644582400 |
| 19 | 1879691760950169600 |
| 20 | 39905092126771200000 |
| 21 | 886664974825728000000 |