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 | 0 |
| 3 | 0 |
| 4 | 3 |
| 5 | 12 |
| 6 | 60 |
| 7 | 360 |
| 8 | 2835 |
| 9 | 24696 |
| 10 | 237384 |
| 11 | 2503440 |
| 12 | 28941165 |
| 13 | 363593340 |
| 14 | 4930388892 |
| 15 | 71759200968 |
| 16 | 1115892704745 |
| 17 | 18465120087120 |
| 18 | 323965034820720 |
| 19 | 6007037150742624 |
| 20 | 117377605956803571 |
| 21 | 2410702829834021820 |
| 22 | 51917379915449131020 |