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 | -5 |
| 4 | 1 |
| 5 | 41 |
| 6 | 751 |
| 7 | -461 |
| 8 | -61375 |
| 9 | -114479 |
| 10 | 3197791 |
| 11 | 51784811 |
| 12 | 95861569 |
| 13 | -13289759495 |
| 14 | -88386566449 |
| 15 | 1959369708451 |
| 16 | 39596487031681 |
| 17 | 144047673616289 |
| 18 | -17707296608390465 |
| 19 | -244965944457878309 |
| 20 | 5109519579305499521 |
| 21 | 149507697206554889161 |