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 | 6 |
| 3 | 40 |
| 4 | 268 |
| 5 | 1801 |
| 6 | 12120 |
| 7 | 81628 |
| 8 | 550040 |
| 9 | 3707635 |
| 10 | 24997966 |
| 11 | 168573824 |
| 12 | 1136933488 |
| 13 | 7668785996 |
| 14 | 51731557296 |
| 15 | 348991600660 |
| 16 | 2354505179952 |
| 17 | 15885669341751 |
| 18 | 107183855819490 |
| 19 | 723217053276952 |
| 20 | 4880016412621148 |
| 21 | 32929530655094281 |