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 | 6 |
| 4 | 45 |
| 5 | 300 |
| 6 | 2080 |
| 7 | 14196 |
| 8 | 97461 |
| 9 | 667590 |
| 10 | 4576825 |
| 11 | 31367160 |
| 12 | 215001216 |
| 13 | 1473620616 |
| 14 | 10100397385 |
| 15 | 69229018950 |
| 16 | 474503107365 |
| 17 | 3252291758436 |
| 18 | 22291541752096 |
| 19 | 152788493829180 |
| 20 | 1047227932532925 |
| 21 | 7177806988136070 |