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 | 4 |
| 2 | 20 |
| 3 | 112 |
| 4 | 660 |
| 5 | 4004 |
| 6 | 24752 |
| 7 | 155040 |
| 8 | 980628 |
| 9 | 6249100 |
| 10 | 40060020 |
| 11 | 258048960 |
| 12 | 1668903600 |
| 13 | 10829900592 |
| 14 | 70480305440 |
| 15 | 459823234112 |
| 16 | 3006465218196 |
| 17 | 19694758782300 |
| 18 | 129235131438140 |
| 19 | 849311959095600 |
| 20 | 5589126007740660 |
| 21 | 36825913869817380 |
| 22 | 242910890642347200 |