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 | 6 |
| 4 | 35 |
| 5 | 220 |
| 6 | 1623 |
| 7 | 14294 |
| 8 | 144393 |
| 9 | 1605384 |
| 10 | 19295585 |
| 11 | 249938062 |
| 12 | 3485830299 |
| 13 | 52134346004 |
| 14 | 830954821431 |
| 15 | 14031857352270 |
| 16 | 249956799370193 |
| 17 | 4682845238636560 |
| 18 | 92038069890608769 |
| 19 | 1893193762636115990 |
| 20 | 40659808272769543635 |
| 21 | 909744112577077608012 |