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 | 0 |
| 3 | 2 |
| 4 | 2 |
| 5 | 6 |
| 6 | 16 |
| 7 | 20 |
| 8 | 132 |
| 9 | 112 |
| 10 | 1216 |
| 11 | 1440 |
| 12 | 12440 |
| 13 | 25520 |
| 14 | 138048 |
| 15 | 476320 |
| 16 | 1649312 |
| 17 | 9138300 |
| 18 | 21842944 |
| 19 | 182232248 |
| 20 | 345145392 |
| 21 | 3805004296 |
| 22 | 7002149760 |
| 23 | 83299368432 |
| 24 | 180168275232 |
| 25 | 1907968553776 |
| 26 | 5402826994176 |
| 27 | 45597877829600 |