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 | 5 |
| 2 | 25 |
| 3 | 120 |
| 4 | 576 |
| 5 | 2760 |
| 6 | 13225 |
| 7 | 63365 |
| 8 | 303601 |
| 9 | 1454640 |
| 10 | 6969600 |
| 11 | 33393360 |
| 12 | 159997201 |
| 13 | 766592645 |
| 14 | 3672966025 |
| 15 | 17598237480 |
| 16 | 84318221376 |
| 17 | 403992869400 |
| 18 | 1935646125625 |
| 19 | 9274237758725 |
| 20 | 44435542668001 |
| 21 | 212903475581280 |