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 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 45 |
| 6 | 225 |
| 7 | 1575 |
| 8 | 11025 |
| 9 | 99225 |
| 10 | 893025 |
| 11 | 9823275 |
| 12 | 108056025 |
| 13 | 1404728325 |
| 14 | 18261468225 |
| 15 | 273922023375 |
| 16 | 4108832377650 |
| 17 | 69850150420050 |
| 18 | 1187452281465450 |
| 19 | 22561593347843550 |
| 20 | 428670250038780750 |
| 21 | 9002075250814395750 |
| 22 | 189043575317350503750 |