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 | 2 |
| 4 | 6 |
| 5 | 64 |
| 6 | 170 |
| 7 | 2988 |
| 8 | 14616 |
| 9 | 180192 |
| 10 | 1934712 |
| 11 | 21673200 |
| 12 | 300266736 |
| 13 | 4220710272 |
| 14 | 61785461712 |
| 15 | 1003589762784 |
| 16 | 17448621367680 |
| 17 | 327598207658496 |
| 18 | 6279739240655232 |
| 19 | 134169095009652480 |
| 20 | 2817563310900129024 |
| 21 | 64570676279407718400 |
| 22 | 1547773850801172960000 |
| 23 | 38824156236466815920640 |