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 | 24 |
| 4 | 192 |
| 5 | 1880 |
| 6 | 21312 |
| 7 | 266504 |
| 8 | 3469312 |
| 9 | 42094656 |
| 10 | 297625600 |
| 11 | -8727514752 |
| 12 | -659406274560 |
| 13 | -31019532622208 |
| 14 | -1314656227540992 |
| 15 | -54314985911216640 |
| 16 | -2248955319931633664 |
| 17 | -94369141109824233472 |
| 18 | -4028982346754921594880 |
| 19 | -175032005028072692797440 |