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 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 90 |
| 6 | 645 |
| 7 | 5355 |
| 8 | 50505 |
| 9 | 532980 |
| 10 | 6219045 |
| 11 | 79469775 |
| 12 | 1103335695 |
| 13 | 16533226710 |
| 14 | 265888247625 |
| 15 | 4566885297975 |
| 16 | 83422361847825 |
| 17 | 1614626682669000 |
| 18 | 33003508539026025 |
| 19 | 710350201433547675 |
| 20 | 16057073233633006575 |