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 | 4 |
| 3 | 18 |
| 4 | 168 |
| 5 | 1830 |
| 6 | 24540 |
| 7 | 388122 |
| 8 | 7084560 |
| 9 | 146650446 |
| 10 | 3395460900 |
| 11 | 86962122786 |
| 12 | 2441210321880 |
| 13 | 74542218945558 |
| 14 | 2459830123779756 |
| 15 | 87236196407090730 |
| 16 | 3308881779086345760 |
| 17 | 133667058288336876894 |
| 18 | 5729380391745420070068 |