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 | 9 |
| 4 | 40 |
| 5 | 265 |
| 6 | 1956 |
| 7 | 18529 |
| 8 | 183520 |
| 9 | 2226753 |
| 10 | 28663300 |
| 11 | 421589641 |
| 12 | 6696832704 |
| 13 | 117283627201 |
| 14 | 2190260755060 |
| 15 | 44645172510345 |
| 16 | 964646320357696 |
| 17 | 22317294448547329 |
| 18 | 547594529028427908 |
| 19 | 14246751684203363593 |
| 20 | 390309056795283743200 |
| 21 | 11276891642831796476481 |