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 | 84 |
| 4 | 858 |
| 5 | 9724 |
| 6 | 117572 |
| 7 | 1485800 |
| 8 | 19389690 |
| 9 | 259289580 |
| 10 | 3534526380 |
| 11 | 48932534040 |
| 12 | 686119227300 |
| 13 | 9723892802904 |
| 14 | 139067101832008 |
| 15 | 2004484433302736 |
| 16 | 29089272078453818 |
| 17 | 424672260824486220 |
| 18 | 6232570989814602524 |
| 19 | 91901608649243484728 |
| 20 | 1360850743459951600780 |