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 | 13 |
| 3 | 149 |
| 4 | 1490 |
| 5 | 13624 |
| 6 | 117920 |
| 7 | 987568 |
| 8 | 8111200 |
| 9 | 65866496 |
| 10 | 531372800 |
| 11 | 4270866688 |
| 12 | 34254920192 |
| 13 | 274425014272 |
| 14 | 2197077311488 |
| 15 | 17583865032704 |
| 16 | 140702055981056 |
| 17 | 1125749585477632 |
| 18 | 9006563605151744 |
| 19 | 72054913990721536 |
| 20 | 576449482336632832 |
| 21 | 4611638739487686656 |