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 | 3 |
| 4 | 24 |
| 5 | 175 |
| 6 | 1386 |
| 7 | 12397 |
| 8 | 125664 |
| 9 | 1431261 |
| 10 | 18099300 |
| 11 | 251194911 |
| 12 | 3788383248 |
| 13 | 61584927495 |
| 14 | 1072118178768 |
| 15 | 19882255276485 |
| 16 | 391068812992512 |
| 17 | 8128569896422821 |
| 18 | 177984169080865992 |
| 19 | 4094103029211918567 |
| 20 | 98692513234032009600 |
| 21 | 2487731188418039207007 |