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 | 1 |
| 2 | 3 |
| 3 | 17 |
| 4 | 135 |
| 5 | 1353 |
| 6 | 16251 |
| 7 | 226857 |
| 8 | 3605775 |
| 9 | 64288209 |
| 10 | 1270969971 |
| 11 | 27603549057 |
| 12 | 653517822615 |
| 13 | 16755529944729 |
| 14 | 462601460800491 |
| 15 | 13685474246611737 |
| 16 | 431948067953729055 |
| 17 | 14489465807596684449 |
| 18 | 514794897939436455651 |