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 | 6 |
| 3 | 9 |
| 4 | 132 |
| 5 | 630 |
| 6 | 6642 |
| 7 | 55440 |
| 8 | 608976 |
| 9 | 6790392 |
| 10 | 85413960 |
| 11 | 1145077560 |
| 12 | 16600386888 |
| 13 | 256806229680 |
| 14 | 4233767671728 |
| 15 | 74015194485960 |
| 16 | 1368023697469440 |
| 17 | 26649263762049600 |
| 18 | 545697922821501888 |
| 19 | 11717708270380421760 |
| 20 | 263276186128105633920 |