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 | 4 |
| 5 | 0 |
| 6 | 0 |
| 7 | 70 |
| 8 | 560 |
| 9 | 0 |
| 10 | 2800 |
| 11 | 92400 |
| 12 | 369600 |
| 13 | 200200 |
| 14 | 19619600 |
| 15 | 252252000 |
| 16 | 695094400 |
| 17 | 5717712000 |
| 18 | 171531360000 |
| 19 | 1307259553600 |
| 20 | 4852431584000 |
| 21 | 136882025280000 |
| 22 | 2175699958432000 |
| 23 | 12698089211808000 |
| 24 | 150837908212992000 |
| 25 | 3848134863773200000 |