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 | 1 |
| 3 | 5 |
| 4 | 34 |
| 5 | 258 |
| 6 | 2172 |
| 7 | 20220 |
| 8 | 207000 |
| 9 | 2315880 |
| 10 | 28143360 |
| 11 | 369411840 |
| 12 | 5210956800 |
| 13 | 78636096000 |
| 14 | 1264324723200 |
| 15 | 21579740582400 |
| 16 | 389730550809600 |
| 17 | 7425628898688000 |
| 18 | 148865650053120000 |
| 19 | 3132539179241472000 |
| 20 | 69036795668865024000 |
| 21 | 1590266397644660736000 |