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 | -1 |
| 4 | -31 |
| 5 | -319 |
| 6 | -2279 |
| 7 | -4199 |
| 8 | 269473 |
| 9 | 7155233 |
| 10 | 114846641 |
| 11 | 920526641 |
| 12 | -18415853279 |
| 13 | -1115017249631 |
| 14 | -31675298017271 |
| 15 | -526379460621559 |
| 16 | 2394778195929281 |
| 17 | 603748739138745281 |
| 18 | 27895091311964499553 |
| 19 | 769764386129113157473 |
| 20 | 6164705700089328588481 |