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 | 2 |
| 2 | 10 |
| 3 | 70 |
| 4 | 588 |
| 5 | 5544 |
| 6 | 56628 |
| 7 | 613470 |
| 8 | 6952660 |
| 9 | 81662152 |
| 10 | 987369656 |
| 11 | 12228193432 |
| 12 | 154532114800 |
| 13 | 1986841476000 |
| 14 | 25928281261800 |
| 15 | 342787130211150 |
| 16 | 4583937702039300 |
| 17 | 61923368957373000 |
| 18 | 844113292629453000 |
| 19 | 11600528392993339800 |
| 20 | 160599522947154548400 |
| 21 | 2238236829690383152800 |