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) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 20 |
| 5 | 132 |
| 6 | 1076 |
| 7 | 10404 |
| 8 | 116180 |
| 9 | 1469892 |
| 10 | 20766836 |
| 11 | 323924964 |
| 12 | 5527326740 |
| 13 | 102396386052 |
| 14 | 2046350191796 |
| 15 | 43876822764324 |
| 16 | 1004631156809300 |
| 17 | 24463049576172612 |
| 18 | 631213045618035956 |
| 19 | 17203155473859536484 |