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 | 1 |
| 3 | 2 |
| 4 | 5 |
| 5 | 24 |
| 6 | 109 |
| 7 | 720 |
| 8 | 4521 |
| 9 | 40320 |
| 10 | 330681 |
| 11 | 3628800 |
| 12 | 36468717 |
| 13 | 479001600 |
| 14 | 5721101541 |
| 15 | 87178291200 |
| 16 | 1205289090513 |
| 17 | 20922789888000 |
| 18 | 328897528901361 |
| 19 | 6402373705728000 |
| 20 | 112769846051251797 |
| 21 | 2432902008176640000 |