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 | 1 |
| 3 | 6 |
| 4 | 17 |
| 5 | 220 |
| 6 | 939 |
| 7 | 20930 |
| 8 | 107393 |
| 9 | 3823416 |
| 10 | 20382195 |
| 11 | 1147905462 |
| 12 | 5519388225 |
| 13 | 515034742404 |
| 14 | 1817577994491 |
| 15 | 323878306632330 |
| 16 | 481078381979649 |
| 17 | 272556878473903344 |
| 18 | -355395800536648605 |
| 19 | 296393140746445749246 |
| 20 | -1420979986049970526335 |