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 | 3 |
| 3 | 21 |
| 4 | 105 |
| 5 | 465 |
| 6 | 1953 |
| 7 | 8001 |
| 8 | 32385 |
| 9 | 130305 |
| 10 | 522753 |
| 11 | 2094081 |
| 12 | 8382465 |
| 13 | 33542145 |
| 14 | 134193153 |
| 15 | 536821761 |
| 16 | 2147385345 |
| 17 | 8589737985 |
| 18 | 34359345153 |
| 19 | 137438167041 |
| 20 | 549754241025 |
| 21 | 2199020109825 |
| 22 | 8796086730753 |
| 23 | 35184359505921 |