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 | 1 |
| 2 | 4 |
| 3 | 52 |
| 4 | 2080 |
| 5 | 251680 |
| 6 | 91611520 |
| 7 | 100131391360 |
| 8 | 328430963660800 |
| 9 | 3232089113385932800 |
| 10 | 95424198983606279987200 |
| 11 | 8452007576574959037306265600 |
| 12 | 2245867453247498115393020895232000 |
| 13 | 1790317944898228845164815929864036352000 |