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 | 2 |
| 3 | 3 |
| 4 | 44 |
| 5 | 210 |
| 6 | 3054 |
| 7 | 27300 |
| 8 | 449952 |
| 9 | 6020784 |
| 10 | 115381080 |
| 11 | 2053568880 |
| 12 | 45733246536 |
| 13 | 1010390340960 |
| 14 | 25916586868704 |
| 15 | 680621684914080 |
| 16 | 19881379012231680 |
| 17 | 603034125051738240 |
| 18 | 19833651290982164544 |
| 19 | 680927283288289169280 |
| 20 | 24953207662252739030400 |