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 | 0 |
| 5 | 5 |
| 6 | 15 |
| 7 | 70 |
| 8 | 420 |
| 9 | 3024 |
| 10 | 28350 |
| 11 | 272250 |
| 12 | 2875950 |
| 13 | 33333300 |
| 14 | 420840420 |
| 15 | 5763671550 |
| 16 | 84799915200 |
| 17 | 1334007397800 |
| 18 | 22343877115560 |
| 19 | 396971840865600 |
| 20 | 7456250728017000 |
| 21 | 147612122975772000 |
| 22 | 3071792315894841000 |
| 23 | 67030983483724953000 |
| 24 | 1530448652869851191400 |