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 | 1 |
| 2 | 6 |
| 3 | 42 |
| 4 | 315 |
| 5 | 2541 |
| 6 | 21931 |
| 7 | 201761 |
| 8 | 1971627 |
| 9 | 20401115 |
| 10 | 222886237 |
| 11 | 2564378397 |
| 12 | 30996823039 |
| 13 | 392772620555 |
| 14 | 5206946927601 |
| 15 | 72084153595073 |
| 16 | 1040323636265431 |
| 17 | 15627180533214417 |
| 18 | 243970019981427565 |
| 19 | 3953119943277152705 |
| 20 | 66394925299770846495 |
| 21 | 1154518082416143179150 |