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 | 1 |
| 4 | 6 |
| 5 | 42 |
| 6 | 402 |
| 7 | 5381 |
| 8 | 112776 |
| 9 | 3935471 |
| 10 | 240684836 |
| 11 | 26449057257 |
| 12 | 5289513580458 |
| 13 | 1939502108505917 |
| 14 | 1311274498490104492 |
| 15 | 1642800188822966309834 |
| 16 | 3831285832174735713684706 |
| 17 | 16703340559932677463553709189 |
| 18 | 136661710199022168890320488632600 |
| 19 | 2105815888079982128884579271408161673 |
| 20 | 61310553163194788144046000967760340771668 |