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 | 1 |
| 5 | 7 |
| 6 | 36 |
| 7 | 228 |
| 8 | 1647 |
| 9 | 13507 |
| 10 | 124268 |
| 11 | 1267542 |
| 12 | 14196477 |
| 13 | 173197024 |
| 14 | 2286200718 |
| 15 | 32464050199 |
| 16 | 493453563029 |
| 17 | 7993947721071 |
| 18 | 137495900802423 |
| 19 | 2502425394604113 |
| 20 | 48046567576398986 |
| 21 | 970540665043259525 |