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 | 1 |
| 2 | 4 |
| 3 | 23 |
| 4 | 144 |
| 5 | 997 |
| 6 | 7304 |
| 7 | 55646 |
| 8 | 436320 |
| 9 | 3497846 |
| 10 | 28538852 |
| 11 | 236203518 |
| 12 | 1978290648 |
| 13 | 16735471979 |
| 14 | 142789868112 |
| 15 | 1227339581084 |
| 16 | 10617748941840 |
| 17 | 92377468226466 |
| 18 | 807769888050640 |
| 19 | 7095187345173620 |
| 20 | 62574408414192220 |
| 21 | 553881698543850337 |