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) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 2 |
| 6 | 6 |
| 7 | 46 |
| 8 | 354 |
| 9 | 3106 |
| 10 | 29926 |
| 11 | 315862 |
| 12 | 3628906 |
| 13 | 45132474 |
| 14 | 604534846 |
| 15 | 8680957902 |
| 16 | 133082437730 |
| 17 | 2169964347282 |
| 18 | 37505486702678 |
| 19 | 685046187718022 |
| 20 | 13186335387855770 |
| 21 | 266816610979894058 |
| 22 | 5662225862272325550 |