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 | 6 |
| 3 | 27 |
| 4 | 156 |
| 5 | 1110 |
| 6 | 8322 |
| 7 | 70098 |
| 8 | 646272 |
| 9 | 6333336 |
| 10 | 66712680 |
| 11 | 745731360 |
| 12 | 8780828328 |
| 13 | 108873486072 |
| 14 | 1413807287760 |
| 15 | 19157627737080 |
| 16 | 270460073295360 |
| 17 | 3965693824244160 |
| 18 | 60266513065134528 |
| 19 | 947644484349584448 |
| 20 | 15389579447794454400 |
| 21 | 257702782790624613120 |