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 | 0 |
| 1 | 0 |
| 2 | 6 |
| 3 | 30 |
| 4 | 140 |
| 5 | 560 |
| 6 | 2058 |
| 7 | 7098 |
| 8 | 23472 |
| 9 | 75372 |
| 10 | 237182 |
| 11 | 735878 |
| 12 | 2260596 |
| 13 | 6896136 |
| 14 | 20933778 |
| 15 | 63325170 |
| 16 | 191089112 |
| 17 | 575626052 |
| 18 | 1731858246 |
| 19 | 5206059774 |
| 20 | 15640198620 |
| 21 | 46966732320 |
| 22 | 140996664986 |
| 23 | 423191320490 |
| 24 | 1269993390720 |