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 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 88 |
| 5 | 470 |
| 6 | 2724 |
| 7 | 17010 |
| 8 | 113712 |
| 9 | 809262 |
| 10 | 6101820 |
| 11 | 48540778 |
| 12 | 405935688 |
| 13 | 3557404838 |
| 14 | 32577733972 |
| 15 | 310987560930 |
| 16 | 3087723669600 |
| 17 | 31823217868318 |
| 18 | 339845199259500 |
| 19 | 3754422961010522 |
| 20 | 42843681016834680 |
| 21 | 504339820818380694 |