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) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 12 |
| 5 | 70 |
| 6 | 442 |
| 7 | 3108 |
| 8 | 24216 |
| 9 | 208586 |
| 10 | 1972904 |
| 11 | 20373338 |
| 12 | 228346522 |
| 13 | 2763212980 |
| 14 | 35926266244 |
| 15 | 499676669254 |
| 16 | 7405014187564 |
| 17 | 116511984902094 |
| 18 | 1940073930857802 |
| 19 | 34087525861589564 |
| 20 | 630296344519286304 |
| 21 | 12235215845125112122 |
| 22 | 248789737587365945992 |